Semiconductor integrated circuit device, process for fabricating the same, and apparatus for fabricating the same

ABSTRACT

Herein disclosed is a semiconductor integrated circuit device fabricating process for forming MISFETs over the principal surface in those active regions of a substrate, which are surrounded by inactive regions formed of an element separating insulating film and channel stopper regions, comprising: the step of for forming a first mask by a non-oxidizable mask and an etching mask sequentially over the principal surface of the active regions of the substrate; the step of forming a second mask on and in self-alignment with the side walls of the first mask by a non-oxidizable mask thinner than the non-oxidizable mask of the first mask and an etching mask respectively; the step of etching the principal surface of the inactive regions of the substrate by using the first mask and the second mask; the step of forming the element separating insulating film over the principal surface of the inactive regions of the substrate by an oxidization using the first mask and the second mask; and the step of forming the channel stopper regions over the principal surface portions below the element separating insulating film of the substrate by introducing an impurity into all the surface portions including the active regions and the inactive regions of the substrate after the first mask and the second mask have been removed.

This application is a Divisional application of application Ser. No.08/230,021, filed Apr. 19, 1994, now U.S. Pat. No. 5,557,147; which is aDivisional application of application Ser. No. 07/954,142, filed Sep.30, 1992, now U.S. Pat. No. 5,331,191; which is a Divisional applicationof application Ser. No. 07/496,330, filed Mar. 20, 1990, now U.S. Pat.No. 5,202,275.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor technology and, moreparticularly, to a technology which is effected when applied to asemiconductor integrated circuit device having a DRAM (i.e., DynamicRandom Access Memory) and to a technology for forming the former.

A memory cell of the DRAM for latching an information of 1 bit! isconstructed of a series circuit between a memory cell selecting MISFETand a information storing capacity element. The memory cell selectingMISFET of the aforementioned memory cell is formed over the principalsurface of the active regions of a semiconductor substrate (or wellregions). The active regions of the semiconductor substrate are formedwithin the region which are surrounded by an element separatinginsulating film (i.e., a field insulating film) formed in the inactiveregions of the aforementioned semiconductor substrate and channelstopper regions. The aforementioned memory cell selecting MISFET has itsgate electrodes connected with word lines extending in a row direction.One of the semiconductor regions of the memory cell selecting MISFET areconnected with complementary data lines. The other semiconductor regionsare connected with one of the electrode of the aforementionedinformation storing capacity element. This information storing capacityelement has its other electrode supplied with a predetermined potential.

The DRAM of this kind has a tendency of being integrated to have alarger capacity and having its memory cells small-sized. In case thesize of the memory cells is reduced, the size of the information storingcapacity element is also reduced so that the amount of charge storage orinformation is dropped. This reduction in the charge storage will dropthe α-ray soft error withstand voltage. Therefore, it is an importanttechnical target of the DRAM having a capacity as large as 1 Mbit! ormore to improve the α-ray soft error withstand voltage.

On the basis of this technical target, there is a tendency that-thestacked structure (i.e,. STC structure) is adopted in the informationstoring capacity element of the memory cell of the DRAM. The informationstoring capacity element of this stacked structure is constructed bylaminating a lower electrode layer, a dielectric film and an upperelectrode layer sequentially. The lower electrode layer is partiallyconnected with other semiconductor region of the memory cell selectingMISFET and has its other portion extended to over the gate electrodes.The upper electrode layer is formed over the aforementioned lowerelectrode layer through a dielectric film. This upper electrode layer isintegrated with the upper electrode layer of the information storingcapacity element of the stacked structure of another adjoining memorycell so that it may be used as a common plate electrode.

Incidentally, the DRAM acting as the information storing capacityelement of the stacked structure and constructing the memory cell isdisclosed in U.S. application Ser. No. 07/246,514 filed on Sep. 19,1988, for example.

SUMMARY OF THE INVENTION

We have found the following problems during the development of a DRAMhaving a capacity as high as 16 Mbits!.

In the DRAM, the separations of the memory cells are accomplished atpresent at an element separating insulating film and channel stopperregions. The element separating insulating film is formed by oxidizingthe principal surface of the inactive regions of the semiconductorsubstrate by using a non-oxidizable mask (of a silicon nitride film)formed over the principal surface of the active regions of thesemiconductor substrate. On the other hand, the channel stopper regionsare formed of an impurity such as B. which is introduced into theprincipal surface portions of the active regions (i.e., only the memorycell array) and the inactive regions of the semiconductor substrate.This impurity is introduced, after the element separating insulatingfilm has been formed, by the ion implantation method using such a highenergy as to transmit the element separating insulating film. Morespecifically, the impurity introduced into the principal surfaceportions of the inactive regions of the semiconductor substrate belowthe element separating insulating film is formed as the aforementionedchannel stopper regions. Since the impurity thus introduced into theprincipal surface portions of the active regions of the semiconductorsubstrate is introduced into deeper regions than the impurity introducedinto the principal surface portions of the inactive regions, it will notadversely affect the memory cells. The process of forming the channelstopper regions using the ion implantation method using that high energyis featured in that it can reduce the narrow channel effect of thememory cell selecting MISFET. Specifically, the aforementioned formingprocess can form the channel stopper regions in self-alignment with theelement separating insulating film so that it can reduce the amount ofdiffusion of the impurity for forming the channel stopper regions to theactive regions.

However, the DRAM being developed by us is intended to have a capacityas large as 16 Mbits! so that it cannot retain the memory cell area andthe memory cell separating area sufficiently. In other words, theaforementioned element separating insulating film has a large amount ofoxidization (i.e., bird's beak) in a transverse direction so that thearea of the element separating insulating film is augmented more thannecessary. This augmentation of the area of the element separatinginsulating film in turn shrinks the memory area more than necessary. Incase, therefore, the aforementioned element separating insulating filmis thinned to reduce the amount of transverse oxidization, the shallowregions of the principal surface portions of the active regions of thesemiconductor substrate are doped with an impurity for forming thechannel stopper regions. The impurity thus introduced into the principalsurface portions of the active regions of the semiconductor substrateenhances the impurity concentration of the surface so that it fluctuatesthe threshold voltage of the memory cell selecting MISFET of the memorycell. As a result, the memory cell area can neither be retained, not canbe shrunk the separating area of the memory cells, thus raising aproblem that the DRAM cannot be highly integrated.

The present invention has the following objects:

(1) to provide a technology capable improving the degree of integrationin a semiconductor integrated circuit device having a storing function;

(2) to provide a technology capable of improving the electricreliability in the aforementioned semiconductor integrated circuitdevice;

(3) to provide a technology capable of improving the soft errorwithstand voltage in the aforementioned semiconductor integrated circuitdevice;

(4) to provide a technology capable of reducing the number offabrication steps in the aforementioned semiconductor integrated circuitdevice;

(5) to provide a technology capable of improving the treating accuracyfor the fabrications in the aforementioned semiconductor integratedcircuit device;

(6) to provide a technology capable of improving the drivability of thesemiconductor elements in the aforementioned semiconductor integratedcircuit device;

(7) to provide a technology capable of improving the fabrication yieldin the aforementioned semiconductor integrated circuit device;

(8) to provide a technology capable of increasing the operating speed inthe aforementioned semiconductor integrated circuit device;

(9) to provide a technology capable of preventing the defects such asthe disconnections of wiring lines in the aforementioned semiconductorintegrated circuit device;

(10) to provide a technology capable of improving a moisture resistancein the aforementioned semiconductor integrated circuit device;

(11) to provide a technology capable of simplifying the steps of formingredundancy fuse elements in the aforementioned semiconductor integratedcircuit device;

(12) to provide a technology capable of improving the quality of filmsto be used in the aforementioned semiconductor integrated circuitdevice; and

(13)to provide an apparatus for fabricating the aforementioned item(12).

The aforementioned and other objects and novel features of the presentinvention will become apparent from the following description to be madewith reference to the accompanying drawings.

Of the invention to be disclosed hereinafter, the reprensentatives willbe briefly summarized in the following.

(1) There is provided a semiconductor integrated circuit devicefabricating process for forming MISFETS over the principal surface inthose active regions of a substrate, which are surrounded by inactiveregions formed of an element separating insulating film and channelstopper regions, comprising: the step of for forming a first mask by anon-oxidizable mask and an etching mask sequentially over the principalsurface of the active regions of said substrate; the step of forming asecond mask on and in self-alignment with the side walls of said firstmask by a non-oxidizable mask thinner than the non-oxidizable mask ofsaid first mask and an etching mask respectively; the step of etchingthe principal surface of said inactive regions of said substrate byusing said first mask and said second mask; the step of forming theelement separating insulating film over the principal surface of theinactive regions of said substrate by an oxidization using said firstmask and said second mask; and the step of forming the channel stopperregions over the principal surface portions below the element separatinginsulating film of said substrate by introducing an impurity into allthe surface portions including the active regions and the inactiveregions of said substrate after said first mask and said second maskhave been removed.

(2) In the foregoing item (1), the step of forming said elementseparating insulating film is accomplished,by a hot oxidization methodwithin a range of 1,050° to 1,150° C.

(3) There is provided a semiconductor integrated circuit device having astoring function, in which a first MISFET forming a memory cell and asecond MISFET forming a peripheral circuit are formed over the principalsurface of the active regions of a substrate in regions surrounded by anelement separating insulating film and channel stopper regions, whereinthe improvement resides: in that said inactive regions are doped with animpurity through said element separating insulating film to form a firstchannel stopper over the principal surface portions of the activeregions of said substrate forming said first MISFET and the inactiveregions surrounding said active regions; and in that the principalsurface portions of the inactive regions of said substrate surroundingsaid active regions for forming the second MISFET are doped with animpurity to form second channel stopper regions of the same conductiontype as that of said first channel stopper regions.

(4) In the foregoing item (3), said first MISFET and said second MISFETare formed over the principal surface portions of the well regions whichare formed in the principal portions of said substrate and which havethe same conduction type as the former but a higher impurityconcentration than that of the former.

(5) There is provided a semiconductor integrated circuit device having astoring function and arranged with the individual elements of a memorycell and a peripheral circuit over the principal surface of theindividual different active regions of a substrate, which are surroundedby channel stopper regions formed over the principal surface portions ofinactive regions of said substrate, wherein the improvement resides: inthat a first channel region enclosing said memory cell and a secondchannel stopper region of the same conduction type as that of said firstchannel stopper region are independently formed at different fabricationsteps; in that the active regions such as the elements of said memorycell and said peripheral circuit or other elements are not arranged inthe boundary regions of said first stopper region and said secondstopper region. Said first channel stopper region and said secondchannel stopper region are superposed or isolated at their boundary.

(6) There is provided a semiconductor integrated circuit deviceincluding a first MISFET having the LDD structure to be used as aninput/output step circuit and a second MISFET having the LDD structureand the same conduction type as that of said first MISFET to be used asan internal circuit, wherein the improvement resides: in that the usedvoltage of said first MISFET is made higher than that of said secondMISFET, wherein the improvement resides: in that the used voltage ofsaid first MISFET is made higher than that of said second MISFET; inthat the gate length of said MISFET is made larger than that of saidsecond MISFET; and in that the gate length of the lightly dopedsemiconductor regions forming the individual LDD structures of saidfirst MISFET and said MISFET are made substantially equal.

(7) There is provided a process for fabricating a semiconductorintegrated circuit device including a first MISFET having a high-voltageLDD structure to be used as an input/output step circuit and a secondMISFET having a low-voltage LDD structure and the same conduction typechannel as that of said first MISFET to be used as an internal circuit,comprising: the step of forming the gate insulating films and gateelectrodes of said first MISFET and said second MISFET at a common stepover the principal surface of the different active regions of asubstrate; the step of forming lightly doped semiconductor regionshaving the LDD structure at a common step over the principal surfaceportions of the individual active regions of said substrate inself-alignment with the individual gate electrodes of said first MISFETand said second MISFET; the step of forming side wall spacers at acommon step on the side walls of the individual gate electrodes of saidfirst MISFET and said second MISFET; and the step of forming highlydoped semiconductor regions on the principal surface portions of theindividual active regions of said substrate in self-alignment with theindividual side wall spacers of said first MISFET and said secondMISFET.

(8) There is provided a semiconductor integrated circuit deviceincluding an n-channel MISFET having the LDD structure and a p-typeMISFET having the LDD structure, wherein the gate length of side wallspacers, which are formed on and in self-alignment with the gateelectrodes of said p-channel MISFET, is made larger than that of sidewall spacers which are formed on and in self-alignment with the sidewalls of the gate electrodes of said n-channel MISFET.

(9) There is provided a process for fabricating a semiconductorintegrated circuit device comprising a DRAM including: a memory cellconstructed of a series circuit of a memory cell selecting MISFET and aninformation storing capacity element of the stacked structure; and acomplementary MISFET having the LDD structure and constructing aperipheral circuit, comprising: the step of sequentially forming theindividual gate insulating films and gate electrodes of the memory cellselecting MISFET of said memory cell and the n-channel MISFET and p-typeMISFET of said peripheral circuit; the step of forming lightly dopedsemiconductor regions in self-alignment with said gate electrodes forforming the individual LDD structures of said memory cell selectingMISFET, said n-channel MISFET and said p-channel MISFET; the step offorming a first side wall spacer on the side walls of the individualgate electrodes of said memory cell selecting MISFET, said n-type MISFETand said p-channel MISFET; the step of forming the highly dopedsemiconductor regions of said n-channel MISFET in self-alignment withsaid first side wall spacer; the step of forming an information storingcapacity element of a stacked structure of said memory cell; the step offorming a second side wall spacer on the side walls of the gateelectrodes of said p-channel MISFET through said first side wall spacerand in self-alighment with said gate electrodes; and the step of formingthe highly doped semiconductor regions of said p-channel MISFET inself-alignment-with said second side wall spacer.

(10) In the foregoing item. (9), further comprised is the step offorming an interlayer insulating film after the step of forming thehighly doped semiconductor regions of said n-type MISFET and before thestep of forming the information storing capacity element having thestacked structure of said memory cell, and wherein said second side wallspacer is formed of said interlayer insulating film after saidinterlayer insulating film has been formed.

(11) There is-provided a semiconductor integrated circuit deviceincluding a DRAM having a memory cell constructed of a series circuitbetween a memory cell selecting MISFET and a information storingcapacity element having a stacked structure, wherein the improvementresides in that the lower electrode layer of said information storingcapacity element of the stacked structure at the side to be connectedwith one of the semiconductor regions of said memory cell selectingMISFET is constructed of the composite film which is prepared bysequentially laminating a silicon film lightly doped with an impurityfor reducing the resistance and a silicon film highly doped with saidimpurity.

(12) There is provided a process for fabricating a semiconductorintegrated circuit device having a memory cell constructed of a seriescircuit between a memory cell selecting MISFET and a information storingcapacity element having a stacked structure, comprising: the step ofdoping a first-layer silicon film with an impurity for reducing.aresistance after said first-layer silicon film has been deposited allover the surface of a substrate including the surface of said memorycell selecting MISFET; the second step of doping a second-layer siliconfilm with an impurity for reducing the resistance after saidsecond-layer silicon film has been deposited all over said first-layersilicon film; and the step of forming the lower electrode layer of saidinformation storing capacity element having the stacked structure bysubjecting said second-layer silicon film and said first-layer siliconfilm individually and sequentially to a predetermined patterning by ananisotropic etching.

(13) There is provided a process for fabricating semiconductorintegrated circuit device including a DRAM having a memory cellconstructed of a series circuit between a memory cell selecting MISFEThaving one of its semiconductor regions connected with data lines and ainformation storing capacity element having a stacked structure andprepared by laminating a lower electrode, a dielectric film and an upperelectrode layer formed over said memory cell selecting MISFETsequentially, comprising: the step of forming said upper electrode layerby depositing a silicon film over the dielectric film of said memorycell by the CVD method and by patterning said silicon film in apredetermined manner by an anisotropic etching; and the step of forminga silicon oxide film by an oxidizing method over the surface of saidupper electrode layer.

(14) There is provided a semiconductor integrated circuit deviceincluding a DRAM having a memory cell constructed of a series circuitbetween a memory cell selecting MISFET having one of its semiconductorregions connected with data lines and a information storing capacityelement having a stacked structure and prepared by laminating a lowerelectrode, a dielectric film and an upper electrode layer formed oversaid memory cell selecting MISFET sequentially, wherein the improvementresides: in that the data lines, which are formed of a composite film bysequentially laminating a silicon film deposited by the CVD method and atransition-metal silicide film through an interlayer insulating filmover the upper electrode layer of said information storing capacityelement having said stacked structure, are constructed; and in that thethickness of the interlayer insulating film between said upper electrodelayer and said data lines is made as large as or larger than one half ofthe gap interposing said upper electrode layer between the lowerelectrode layer of the information storing capacity element of thestacked structure of said memory cell and the lower electrode layer ofsaid information storing capacity element of said stacked structure ofanother memory cell adjoining the former with the minimum gap.

(15) There is provided a semiconductor integrated circuit device havinga storing function and including: complementary data lines, word linesand column select signals lines over a memory cell array; andtwo-layered wiring layers in the regions of a peripheral circuit of saidmemory cell array, wherein the improvement resides: in that thecomplementary data lines over said memory cell array are formed of acomposite film prepared by sequentially laminating a silicon film and atransition-metal silicide film deposited by the CVD method; in that saidcolumn select signal lines are formed of a transition-metal filmdeposited by the sputtering method over said complementary data lines;in that said word lines are formed of an aluminum film or its alloy filmdeposited by the sputtering method over said column select signal lines;in that the same conducting layer as said word lines and the sameconducting layer as the column select signals underlying the former areconnected through a transition metal film buried by the selective CVDmethod in the connecting holes formed in the interlayer insulating filminbetween; in that the lower wiring lines of the two wiring lines of theregions of said peripheral circuit are formed of the same conductinglayer as said column select signal lines whereas the upper wiring linesof said two wiring layers are formed of the same conducting layer assaid word lines; and in that the upper and lower wiring lines of saidtwo wiring layers are individually connected through a transition metalfilm buried in said connecting holes by the selective CVD method.

(16) There is provided a semiconductor integrated circuit deviceincluding: a transition-metal film buried by the selective CVD method inconnecting holes formed in an underlying interlayer insulating film; anda Si-added aluminum alloy wiring lines extending over said interlayerinsulating film and connected with said transition-metal film, whereinthe improvement resides in that a transition-metal silicide film or atransition-metal nitride film is formed between said aluminum alloywiring lines and said underlying interlayer insulating film includingthe gaps between said transition-metal film buried in said connectinghole sand said aluminum alloy wiring lines.

(17) There is provided a semiconductor integrated circuit deviceincluding: a transition-metal film buried by the selective CVD method inconnecting holes formed in an underlying interlayer insulating film; andCu-added aluminum alloy wiring lines connected with saidtransition-metal film and extending over said interlayer insulatingfilm, wherein the improvement resides in that a transition-metal nitridefilm acting as a barrier is formed between the transition-metal filmburied in said connecting holes and said aluminum-alloy wiring lines.

(18) In the foregoing items (16) and (17), a TiN film having a crystalorientation (200) is interposed between said transition-metal filmburied in said connecting holes and said aluminum-alloy wiring lines.

(19) There is provided a semiconductor integrated circuit device havinga passivation film formed over a wiring layer formed of an aluminum filmor its alloy film, wherein the improvement resides: in that saidpassivation film is formed of a composite film prepared by sequentiallylaminating a silicon oxide film deposited by the conformal plasma CVDmethod using tetraethoxysilane gases as its source gases and a siliconnitride film deposited by the plasma CVD method; and in that the lowersilicon oxide film of said passivation film is formed to have athickness as large as or more than one half of the wiring gap of theregions in which the aspect ratio of said wiring gap and the thicknessof said wiring lines is 1 or more.

(20) There is provided a process for fabricating asemiconductor-integrated circuit device having complementary MISFETs,comprising: the step of forming a first conductor region of a secondconduction type having an impurity concentration for setting thethreshold voltage of a first MISFET of a first conduction type channeland electrically separated from another region and a secondsemiconductor region of the first conduction type having an impurityconcentration for setting the threshold voltage of a second MISFET ofthe second conduction type channel individually in the principal surfaceportions of the different regions of a semiconductor substrate; and thestep of setting the threshold voltage of a third MISFET of the firstconduction type channel different from the threshold voltage of saidfirst MISFET by doping the principal surface portions of the regions ofsaid first semiconductor regions different from said first MISFET with athreshold voltage adjusting impurity, and setting the threshold voltageof a fourth MISFET of a second conduction type channel different fromthe threshold voltage of said second MISFET by doping the principalsurface portions of said second semiconductor regions different fromsaid second MISFET with a threshold voltage adjusting impurity.

(21) In the foregoing item (20), said first semiconductor region andsaid second semiconductor region are well regions which are individuallyformed in self-alignment with the principal surface portions of saidsemiconductor substrate.

(22) There is provided a process for fabricating a semiconductorintegrated circuit device, in which first and second MISFETs forgenerating a reference voltage and another third MISFET are individuallyformed to have a common conduction type channel, comprising: the step offorming a substrate or a well region with an impurity concentration forsetting the threshold voltage of said first MISFET for generating saidreference voltage; the step of setting the threshold voltage of saidsecond MISFET for generating said reference voltage or the thresholdvoltage of said third MISFET by doping the regions of said substrate orsaid well regions different from said first MISFET with a thresholdvoltage adjusting impurity; and the step of setting the thresholdvoltage of said third MISFET or the threshold voltage of said secondMISFET for generating said reference voltage by doping with the regionsof said substrate or said well regions different from said first MISFET,said second MISFET or said third MISFET with a threshold voltageadjusting impurity.

(23) There is provided a semiconductor integrated circuit deviceincluding a DRAM arranged with memory cells formed of a series circuitbetween a memory cell selecting MISFET at the intersection betweencomplementary data lines and word lines and a information storingcapacity element having a stacked structure, and a laser cuttingredundancy fuse element for relieving the defective ones of saidcomplementary data lines or said word lines, wherein the improvementresides: in that said complementary data lines are formed of a compositefilm prepared by sequentially laminating a silicon film deposited by theCVD method and a transition-metal silicide film; and in that said lasercutting redundancy fuse elements are formed of a conducting layer sharedwith said complementary data lines.

(24) There is provided a process for depositing a conducting film or aninsulating film over the surface of a semiconductor wafer or the surfaceof a silicon film deposited on the surface of said semiconductor wafer,comprising: the step of exposing the surface of said semiconductor waferor the surface of said silicon film to the outside by cleaning thesurface of said semiconductor wafer or the surface of said silicon filmin a vacuum system; and the step of depositing said conducting film orsaid insulating film on the surface of said semiconductor wafer or thesurface of said silicon film in the vacuum system shared with saidcleaning step.

(25) There is provided a film depositing process for depositing aninsulating film either on the surface of a semiconductor wafer or thesurface of a silicon film deposited on the surface of said semiconductorwafer, comprising: the step of exposing the surface of saidsemiconductor wafer or the surface of said silicon film by cleaning thesurface of said semiconductor wafer or the surface of said silicon filmin a vacuum system by an anisotropic etching using a halogen compound;the step of irradiating the exposed surface of said semiconductor waferor the exposed surface of said silicon film with an ultraviolet ray inthe vacuum system shared with said cleaning step; and the step ofdepositing said insulating film on the surface of said semiconductorwafer or the surface of said silicon film in the vacuum system sharedwith said cleaning step.

(26) There is provided a film depositing process for depositing asilicon film on an underlying surface having a stepped shape,comprising: the step of alternately depositing a plurality of layers ofa silicon film containing an impurity for reducing the resistance and asilicon film containing none of said impurity over said underlyingsurface; and the step of diffusing said impurity from said silicon filmcontaining said impurity to said silicon film containing none of saidimpurity by subjecting the laminated silicon films to a heat treatment.

(27) There is provided a film depositing process for depositing asilicon film on an underlying surface having a stepped shape, whereinthe improvement resides: in that a silicon film containing no impurityas a result of thermal decompositions is deposited by feeding silanegases at a constant flow rate in a vacuum system for depositing saidsilicon film; and in that said deposited silicon film is periodicallydoped with phosphor by feeding phosphine gases by increasing ordecreasing the flow rate periodically in said vacuum system.

(28) There is provided an alignment process for aligning differentthree-layer patterns in an X direction and in a Y direction, wherein theimprovement resides: in that the second-layer pattern is aligned in theX direction and in the Y direction with respect to the first-layerpattern underlying the former; and in that the third-layer patternformed over said second-layer pattern is aligned in the X direction andin the Y direction with respect to the second-layer pattern underlyingthe former and in the Y direction and in the X direction with respect tothe first-layer pattern underlying the former.

(29) There is provided a semiconductor integrated circuit device inwhich an interlayer insulating film is formed over an underlying surfacehaving a stepped shape, in which first connecting holes are formed inthe upper regions of the stepped shape of said underlying surface ofsaid interlayer insulating film whereas second connecting holes areformed in the lower regions of said stepped shape, and in which wiringlines are so extended over said interlayer insulating film that they maybe connected with conducting films individually buried in said firstconnecting holes and said second connecting holes, wherein theimprovement resides: in that the conducting films individually buried insaid first connecting holes and said second connecting holes are formedof a transition-metal film which is made of a common conducting layerdeposited by the selective CVD method; and in that said transition-metalfilm is deposited to have a thickness as large as the depth of saidshallow first connecting holes.

(30) There is provided a semiconductor integrated circuit device havingits wiring lines formed of a transition-metal film deposited over anunderlying insulating film by the CYD method, wherein the improvementresides in that a transition-metal film of substantially the same kindas that of said wiring lines deposited by the sputtering method isformed between said underlying insulating film and said wiring lines.

(31) There is provided a semiconductor integrated circuit device havinga DRAM arranged at the intersections between complementary data linesand word lines with memory cells each constructed of a series circuitbetween a memory cell selecting MISFET and a information storingcapacity element having a stacked structure, in which a lower electrodelayer, a dielectric film,and an upper electrode layer are sequentiallylaminated, wherein the improvement resides in that an intermediateconducting film having its portion formed in self-alignment with one ofthe semiconductor regions of said memory cell selecting MISFET and itsother portion led out over the gate electrodes of said memory cellselecting MISFET and formed below and separately of the lower electrodelayer of said information storing capacity element of said stackedstructure is formed between said complementary data lines and said onesemiconductor region.

(32) In the foregoing item (31), said intermediate conducting film isformed to have a smaller thickness than that of the lower electrodelayer of said information storing capacity element of said stackedstructure.

(33) In the DRAM of the foregoing item (31), an intermediate conductingfilm formed of the conducting layer shared with the intermediateconducting film formed in said memory cells is interposed between thesemiconductor regions of the MISFETs constructing the peripheral circuitof said DRAM and the wiring lines connected with the former.

According to the aforementioned means (1), the non-oxidizable mask ofthe aforementioned second mask can be thinned to reduce the amount oftransverse oxidization of the element separating insulating film so thatthe element separating insulating film can be small-sized and thickenedto increase the isolation size of the MISFETs in the depthwise directionof the substrate thereby to enhance the separatability of the MISFETs.The element separating insulating film can be thickened. Thus, when animpurity for forming the aforementioned channel stopper regions is to beintroduced, the impurity to be introduced into the principal surfaceportions of the active regions of the substrate can be introduced deepinto the substrate to reduce the fluctuations of the threshold voltageof the MISFETs as a result of the introduction of the aforementionedimpurity.

According to the aforementioned second means (2), when the elementseparating insulating film is to be formed, the fluidicity of thesilicon oxide film as a result of the hot oxidization method can bepromoted to reduce the stress which is established between the elementseparating insulating film and the principal surface of the inactiveregions of the substrate. As a result, it is possible to reduce theoccurrences of the crystal defects at the corners of the grooves whichare formed in the principal surface of the inactive regions of thesubstrate.

According to the aforementioned means (3), the threshold voltage of theparasitic MOSes can be raised at the aforementioned first channelstopper regions to retain the separating ability between the memorycells and the first MISFET and surrounding elements forming the former.At the same time, the aforementioned first channel stopper regions areformed in self-alignment with the aforementioned element separatinginsulating film, and the impurity for forming the first channel stopperregions can be made to have a small amount of diffusion to the activeregions thereby to reduce the narrow channel effect of theaforementioned first MISFET. Since the impurity for forming theaforementioned second channel stopper regions is introduced only intothe inactive regions but not the active regions for forming theaforementioned second MISFET, the influences of the substrate effect canbe reduced to reduce the fluctuations of the threshold voltage. Sincethe second MISFET is formed to have a larger size than the first MISFET,it has a relative small amount of diffusion of the active regions forforming the second channel stopper regions to the active regions so thatit raises substantially no narrow channel effect. Since, moreover, thesecond MISFET does not have its active regions doped with the impurityfor forming the second channel stopper regions to reduce the impurityconcentration in the surface of the aforementioned active regions, thethreshold voltage can be reduced to augment the drivability. especiallyin case the second MISFET is sued as an output step circuit, the outputsignal level can be sufficiently retained.

According to the aforementioned means (4), the aforementioned wellregions raise the impurity concentrations in the channel forming regionsof the first and second MISFETs so that they can reduce the shortchannel effect. Since the difference between the impurity concentrationsof the well regions and the aforementioned substrate, it is possible toimprove the α-ray soft error withstand voltage especially of the memorycells. In case, moreover, the second MISFETs construct the columnaddress decoder circuit or the sense amplifier circuit, they canlikewise improve the α-ray soft error withstand voltage.

According to the aforementioned means (5), in case the aforementionedfirst channel stopper regions and second channel stopper regions areindividually superposed at the aforementioned boundary regions, theirimpurity concentrations are increased. Since, however, the activeregions are not arranged in the boundary regions, the junction withstandvoltage between the substrate and the elements can be improved. In case,on the other hand, the first channel stopper regions and the secondchannel stopper regions are individually isolated at the aforementionedboundary regions, these boundary regions become liable to be formed witha large inversion layer corresponding to their area. If the activeregions are present in the boundary regions, the area of the elements tobe formed in the active regions is apparently increased by the additionof the aforementioned inversion layer so that the flow rate of theleakage current is augmented at the junction portions between thesubstrate and the elements. Since, however, the active regions are notarranged in the boundary regions, the flow rate of the leakage currentcan be reduced at the junction portions.

According to the aforementioned means (6), the aforementioned firstMISFET has its hot carrier withstand voltage improved by enlarging itsgate length so that the aging of the threshold voltage can be reduced toimprove the electric characteristics. At the same time, theaforementioned second MISFET is enabled to reduce the power consumptionby using a low voltage while retaining the hot carrier withstand voltageby using the low voltage. Since, moreover, the MISFET has its gatelength enlarged and since the second MISFET is enabled to improve thehot carrier withstand voltage by using the low voltage, the gate lengthof the lightly doped semiconductor regions forming the aforementionedLDD structure can be independently controlled to substantially equalizethe gate lengths of the individual lightly-doped semiconductor regionsof the first MISFET and the second MISFET.

According to the aforementioned means (7), all the steps of forming theaforementioned first MISFET and second MISFET can be shared to form theindividual side wall spacers at the common fabrication step so that thenumber of fabrication steps of the semiconductor integrated circuitdevice can be reduced.

According to the aforementioned means (8), the gate length of the sidewall spacers of the aforementioned n-channel MISFET together with thegate length of the lightly doped semiconductor substrate forming the LDDstructure so that the transmittance conductance of the n-channel MISFETcan be improved to increase the operating speed. At the same time, thegate length of the side wall spacers of the p-channel MISFET can beenlarged to reduce the run-around of the highly doped semiconductorregions forming the source regions and the drain regions to the channelforming regions. As a result, the short channel effect of the p-channelMISFET can be reduced to increase the degree of integration.

According to the aforementioned means (9), the aforementioned n-channelMISFET specifies the gate length of the lightly doped semiconductorregions forming the LDD structure with the single-layered first sidewall spacers so that the gate length of the lightly semiconductorregions can be reduced. The p-channel MISFET regulates the run-around ofthe highly doped semiconductor regions to the channel forming regionswith the multi-layered first and second side wall spacers. After theheat treatment for forming the information storing capacity element ofthe stacked structure of the aforementioned memory cells, the highlydoped semiconductor regions are formed so that the run-around of thehighly doped semiconductor regions to the channel forming regions can befurther reduced.

According to the aforementioned means (10), the step of forming theaforementioned second side wall spacers can be shared with the step offorming the aforementioned interlayer insulating film so that the numberof steps of fabricating the semiconductor integrated circuit device canbe accordingly reduced.

According to the aforementioned means (11), the lower electrode layer ofthe information storing capacity element of the stacked structure of theaforementioned memory cells is so thickened that the area of the sidewalls of the lower electrode layer can be vertically increased. As aresult, the amount of charge storage can be increased to shrink the areaof the memory cells thereby to improve the degree of integration. Sincethe impurity concentration in the surface of the upper silicon film ofthe aforementioned lower electrode layer is high, the amount of chargestorage can be increased to improve the degree of integration likewise.Since, moreover, the impurity concentration of the silicon film of thelower electrode layer can be dropped to reduce the amount of diffusionof the impurity to one of the semiconductor regions of the memory cellselecting MISFET, the short channel effect of the memory cell selectingMISFET can be dropped to shrink the area of the memory cells thereby toimprove the degree of integration better.

According to the aforementioned means (12), even the lower electrodelayer of the information storing capacity element having theaforementioned stacked structure is thickened, the amount of theimpurity introduced thereinto is retained to some extent and uniformedso that the anisotropy of the anisotropic etching can be enhanced whileincreasing the etching rate. This improvement in the anisotropy of theanisotropic etching can shrink the size of the lower electrode layer toshrink the memory cell area thereby to improve the degree ofintegration.

According to the aforementioned means (13), the residual of theaforementioned silicon film left unetched in the stepped portion of theunderlying surface after the patterning of the silicon film can beoxidized by the subsequent oxidization step so that the aforementionedupper electrode layer and data lines can be prevented from being shortedto improve the fabrication yield. Especially if the lower electrodelayer of the information storing capacity element of the stackedstructure is thickened to improve the amount of charge storage, thestepped shape of the underlying surface of the upper electrode layer canbe enlarged to make the aforementioned process effective.

According to the aforementioned means (14), the upper transition-metalsilicide film of the aforementioned data lines is liable to experiencethe mutual diffusions of the impurity. As a result, the flattening ofthe underlying surface of the data lines cannot be promoted, but thethickness of the aforementioned interlayer insulating film can becontrolled on the basis of the size of the gap between the lowerelectrode layers adjoining with the aforementioned minimum gap toflatten the surface of the interlayer insulating films by burying thegap between the lower electrode layers with the interlayer insulatingfilm. As a result, the -data lines can be prevented from being shorteddue to the etching residual left at the stepped portion of theinterlayer insulating film between the lower electrode layers, when thedata lines are to be treated, to improve the electric reliability.

According to the aforementioned means (15), the complementary data lineson the aforementioned memory cell array can be excellent in the heatresistance and the non-oxidizability and can have a high step coverageof the underlying silicon film deposited by the CVD method to reduce thedefects such as the disconnections. The aforementioned column selectsignal lines are formed over the complementary data lines so that theycan be extended substantially straight without avoiding the connectedportions between the complementary data lines and the memory cells. As aresult, the signal transmission speed can be increased to speed up theinformation writing operations and the information reading operations.Since the column select signal lines are formed of a layer differentfrom that of the complementary data lines, the wiring gap between thelower complementary data lines can be shrunk to improve the degree ofintegration. Since the aforementioned word lines (i.e., the shuntingword lines) are made to have a lower resistance than that of the lowercomplementary data lines or the column select signal lines, theirresistance can be reduced to increase the individual speeds of theinformation writing operation and the information reading operation. Thetransition-metal films for connecting the same conducting layer as thecolumn select signal lines and the same conducting layer as the wordlines can compensate the step coverage at the connected portions of thesame conducting layer as the upper word lines to reduce the defects suchas the disconnections of that conducting layer. At the same time, thestress with the underlying transition-metal film can be reduced bymaking the underlying conducting layer of the transition-metal film ofthe same kind. The lower wiring lines of the regions of theaforementioned peripheral circuit, i.e, the direct peripheral circuit(e.g., the sense amplifier circuit or the decoder circuit) of theaforementioned memory cell array can have a high migration withstandvoltage, because it is made of a transition-metal film, to shrink thewiring gap thereby to improve the degree of integration.

According to the aforementioned means (16), the underlying layer of theaforementioned aluminum alloy wiring lines is uniformed over thetransition-metal film buried in the aforementioned connecting hole andthe interlayer insulating film so that the deposition of the Si added tothe aluminum alloy wiring lines, which might otherwise come into theboundary between the transition-metal film buried in the connectingholes and the aluminum alloy wiring lines, can be reduced to reduce theresistance of the aforementioned boundary. Moreover, thetransition-metal silicide film formed below the aforementioned aluminumalloy wiring lines can connect the aluminum alloy wiring lines throughthe cut portions, if made by the migration phenomenon at the aluminumalloy wiring lines, to reduce the defects such as the disconnections ofthe wiring lines.

According to the aforementioned means (17), the alloying reaction due tothe mutual diffusions of the transition metal and the aluminum can beprevented at the boundary between the transition-metal film buried inthe aforementioned connecting holes and the aluminum alloy wiring linesto reduce the resistance of the boundary.

According to the aforementioned means (18), the TiN film having theaforementioned crystal orientation (200) can have a smaller Sideposition than that of the TiN film having a mixed crystal orientationbetween (111) and (299) to reduce the resistance of the aforementionedboundary. Since, moreover, the TiN film having the crystal orientation(200) has a lower specific resistance than that of the TiN film havinganother crystal orientation, the resistance at the boundary can bereduced. Since the film density is high, it is possible to improve theaction as the barrier.

According to the aforementioned means (19), the lower silicon oxide filmof the aforementioned passivation film can be deposited at such a lowtemperature as to melt none of the aforementioned wiring lines and at ahigh step coverage so that the it can flatten the stepped shape to beformed in the aforementioned wiring layer. Thus, the silicon nitridefilm overlying the passivation film and having an excellent moistureresistance can be formed without any cavity based upon theaforementioned stepped shape. As a result, the no cavity is formed inthe upper silicon nitride film of the passivation film to cause nocracking of the aforementioned silicon nitride film and no residual ofthe water content in the cavity so that the moisture resistance of thepassivation film can be improved.

According to the aforementioned means (20), the threshold voltage of theaforementioned first MISFET can be set with the impurity concentrationof the first semiconductor regions, and the threshold voltage of theaforementioned second MISFET can be set with the impurity concentrationof the second semiconductor regions. Thus, the threshold voltage of thefour kinds can be set by the twice introductions of the thresholdvoltage adjusting impurities so that the number of the steps ofintroducing the threshold voltage adjusting impurities can be reduced.

According to the aforementioned means (21), no step of exposing thesurface of the semiconductor substrate other than the aforementionedwell regions can be required to reduce the number of the fabricationsteps accordingly.

According to the aforementioned means (22), the threshold voltage of thefirst MISFET for generating the aforementioned reference voltage can beset with the impurity concentration of the substrate or the wellregions. Thus, the threshold voltages of the three kinds can be set bythe twice introductions of the threshold voltage adjusting impurities toreduce the number of steps of introducing the threshold voltageadjusting impurities.

According to the aforementioned means (23), the aforementionedcomplementary data lines are formed over the aforementioned memory cellselecting MISFET and the information storing capacity element of thestacked structure so that the number of the upper insulating films ofthe aforementioned laser cutting redundancy fuse elements can be reducedto simplify the opening process of the upper insulating films of thelaser cutting redundancy fuse elements. At the same time, theaforementioned composite film formed of the silicon film and thetransition-metal silicide film has a higher laser beam absorptivity thanthat of the wiring lines (e.g., the aluminum wiring lines) formed overthe complementary data lines so that the aforementioned laser cuttingredundancy fuse elements can be easily cut.

According to the aforementioned means (24), the conducting film or theinsulating film can be deposited on the surface of the aforementionedsemiconductor wafer or the surface of the silicon film without beingexposed to the atmosphere, after the natural silicon oxide formed on thesurface of the semiconductor wafer or the surface of the silicon filmhas been removed by the cleaning step. Thus, the aforementioned naturalsilicon oxide film is not left between the surface of the semiconductorwafer or the surface of the silicon film and the aforementionedconducting film or insulating film. As a result, the conduction can beensured between the surface of the semiconductor wafer or the surface ofthe silicon film and the conducting film to be deposited on the surfaceof the former. Moreover, the surface of the semiconductor wafer or thesurface of the silicon film and the insulating film such as thedielectric film deposited on the former can be thinned to an extent tothe aforementioned natural silicon oxide film (or to have a largedielectric constant in case the dielectric film is formed of a siliconnitride film) to increase the amount of charge storage of the capacityelements.

According to the aforementioned means (25), the radicals of the halogenelements sticking to the surface of the semiconductor wafer or thesurface of the silicon film can be removed with the aforementionedultraviolet ray when that surface is cleaned. Thus, it is possible toreduce the leakage current of and the change in the insulating film suchas the silicon nitride film to be deposited on the surface of thesemiconductor wafer or the surface of the silicon nitride film.

According to the aforementioned means (26), in the regions of thestepped shape of the aforementioned underlying surface, the stepcoverage of the silicon film containing the impurity can be compensatedwith the silicon film containing none of the impurity so that thethickness of the silicon film can be uniformed. At the same time, theaforementioned impurity can be diffused from the silicon film containingthe impurity to the silicon film containing no impurity so that themulti-layered silicon film can have its large thickness retained whileuniforming the impurity concentration.

According to the aforementioned means (27), the silicon film containingthe impurity of the foregoing item (26) and the silicon film containingno impurity can be continuously deposited in the common vacuum system sothat the throughput can be improved.

According to the aforementioned means (28), the displacement of thealignment between the aforementioned first-layer pattern andsecond-layer pattern and the displacement of the alignment between thefirst-layer pattern and the second-layer pattern can be substantiallyequalized to reduce the displacement of the alignment between thefirst-layer pattern and the third-layer pattern. As a result, in casethe aforementioned alignment process is applied to the semiconductorintegrated circuit device, the element size can be shrunk to an extentcorresponding to the masking allowance at the fabrication step toimprove the degree of integration of the semiconductor integratedcircuit device.

According to the aforementioned means (29), the transition-metal filmindividually buried in the aforementioned first connecting holes andsecond connecting holes is formed to have a thickness substantiallyequal to the depth of the shallow first connecting holes so that none ofthe transition-metal film will not protrude from the first connectingholes and the second connecting holes. As a result, it is possible toimprove the treating accuracy and the reliability of the aforementionedwiring lines.

According to the aforementioned means (30), the transition-metal filmdeposited by the aforementioned sputtering method has individually highcontactnesses with the aforementioned underlying insulating film andwiring lines so that the contactness between the underlying insulatingfilm and the wiring lines can be improved. At the same time, thetransition-metal film deposited by the sputtering method is formed of atransition-metal film belonging to substantially the same kind as thatof the overlying wiring lines so that the treating accuracy of thewiring lines and the underlying transition-metal film can be improved.

According to the aforementioned means (31), thanks to the interpositionof the aforementioned intermediate conducting film, the memory cell areacan be shrunk to improve the degree of integration to an extentcorresponding to the masking allowance at the fabrication step betweenone of the semiconductor regions of the memory cell selecting MISFET andthe complementary data lines. At the same time, the gap between theintermediate conducting film and the lower electrode layer of theinformation storing capacity element of the stacked structure can beeliminated to increase the area of the lower electrode layerindependently of the intermediate conducting film. Thus, the memory cellarea can be shrunk by increasing the amount of charge storage of theinformation storing capacity element of the stacked structure to improvethe degree of integration.

According to the aforementioned means (32), the information storingcapacity element of the stacked structure can have its lower electrodelayer thickened to increase the vertical area so that the amount ofcharge storage can be improved to shrink the memory cell area andimprove the degree of integration. At the same time, the aforementionedintermediate conducting film can be thinned to simplify the treatment.

According to the aforementioned means (33), the intermediate conductingfilm of the peripheral circuit can be formed at the step of forming theintermediate conducting film formed in the memory cells of the DRAM toreduce the number of fabrication steps.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a section showing an essential portion of the DRAM accordingto an embodiment I of the present invention;

FIG. 2 is a partially sectional perspective view showing a resin-sealedtype semiconductor device for sealing the aforementioned DRAM;

FIG. 3 is a layout diagram showing the chip of the aforementioned DRAM;

FIG. 4 is a circuit diagram showing an equivalent circuit of the memorycell array of the aforementioned DRAM;

FIG. 5 is a top plan view showing an essential portion of the memorycell array of the aforementioned DRAM;

FIGS. 6 and 7 are top plan views showing an essential portion at apredetermined fabrication step of the memory cell array of theaforementioned DRAM;

FIG. 8 is a graph presenting the relations between the target voltageand the specific resistance when the film to be used in theaforementioned DRAM is sputtered;

FIGS. 9 and 10 are graphs presenting the relations of the incidentangles of an X-ray and the X-ray diffraction spectra of theaforementioned film;

FIGS. 11 and 13 are schematic top plan views showing the boundaryregions between the aforementioned memory cell array and a peripheralcircuit;

FIGS. 12 and 14 are enlarged top plan views showing an essential portionof the aforementioned boundary region;

FIG. 15 is a section showing an essential portion at another position ofthe aforementioned DRAM;

FIGS. 16 to 49 are sections showing an essential portion at theindividual fabrication steps of the aforementioned DRAM;

FIG. 50 is a section showing an essential portion of a fuse element ofthe aforementioned DRAM;

FIGS. 51 to 53 are sections showing an essential portion at theindividual fabrication steps of the aforementioned fuse element;

FIG. 54 is a graph presenting the relation between the temperature andthe vacuum pressure of the film used in the aforementioned DRAM;

FIG. 55 presents diagrams plotting the etching characteristics to beused in the aforementioned DRAM;

FIGS. 56 to 58 are sections showing an essential portion of the DRAMaccording to an embodiment II of the present invention;

FIGS. 59 to 60 are sections showing an essential portion of the DRAMaccording to an embodiment III of the present invention;

FIG. 61(A) is a graph presenting the relation between the depositiontime of the film used in the aforementioned DRAM and the gas flow rate;

FIG. 61(B) is a graph presenting the relation between the depositiontime of the aforementioned film and the yield of the reactionby-product;

FIG. 62 is a schematic diagram showing a CVD apparatus according to anembodiment IV of the present invention;

FIGS. 63 and 64 are schematic diagrams showing essential portions of theaforementioned CVD apparatus;

FIG. 65 is a time chart presenting the opening and closing operations ofthe gas valves of the CVD apparatus according to an embodiment V of thepresent invention;

FIG. 66 is a time chart presenting the gas flow rates of theaforementioned CVD apparatus;

FIG. 67 is a schematic diagram showing the aforementioned CVD apparatus;

FIGS. 68 to 71 are sections showing an essential portion at theindividual fabrication steps of the DRAM according to an embodiment VIof the present invention;

FIG. 72 is a top plan view showing an essential portion at apredetermined fabrication step of the DRAM according to an embodimentVII of the present invention;

FIGS. 73 to 76 are sections showing an essential portion at theindividual fabrication steps of the aforementioned pRAM;

FIG. 77 is a top plan view showing an essential portion at apredetermined fabrication step of another example of the aforementionedDRAM;

FIGS. 78 to 80 are sections showing an essential portion at theindividual fabrication steps of another example of the aforementionedDRAM;

FIGS. 81 to 84 are sections showing an essential portion at theindividual fabrication steps of another example of the aforementionedDRAM;

FIGS. 85 to 88 are sections showing an essential portion at theindividual fabrication steps of another example of the aforementionedDRAM;

FIG. 89 is a diagram showing the alignment tree of the DRAM according toan embodiment VIII of the present invention;

FIG. 90 is a section showing an essential portion of the target markportion of the DRAM according to an embodiment IX of the presentinvention;

FIG. 91 is a conceptional diagram showing the photolithographytechnology to be used in the fabrication process of the DRAM accordingto an embodiment X of the present invention;

FIG. 92 is a flow chart showing the steps of the aforementionedphotolithography technology;

FIG. 93 is a diagram showing the structure of a substance to be used inthe photolithography technology;

FIG. 94 is a diagram presenting the characteristics of theaforementioned substance;

FIG. 95 is a diagram for explaining the effects when the aforementionedsubstance is used;

FIG. 96 is a schematic top plan view showing the structure of asemiconductor wafer according to an embodiment XI of the presentinvention;

FIG. 97 is an enlarged top plan view showing the aforementionedsemiconductor wafer;

FIG. 98 is an enlarged top plan view showing the semiconductor wafershown in FIG. 97;

FIG. 99 is a diagram for explaining the effects in case the associativealignment type is applied;

FIG. 100 is a section showing an essential portion of the DRAM 1according to an embodiment XII of the present invention;

FIG. 101 is a section showing an essential portion at a predeterminedfabrication step of the aforementioned DRAM;

FIG. 102 is a section showing an essential portion of the DRAM accordingto an embodiment XIII of the present invention;

FIG. 103 is a graph presenting the relation between the target voltageand the stress when the film used in the aforementioned DRAM issputtered;

FIG. 104 is a section showing an essential portion of the DRAM 1according to an embodiment XIV of the present invention; and

FIGS. 105 and 106 are sections showing an essential portion at theindividual fabrication steps of the aforementioned DRAM.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The structure of the present invention will be described in thefollowing in connection with one embodiment thereof, in which thepresent invention is applied to a DRAM having its memory cellconstructed of a series circuit of a memory cell selecting MISFET and aninformation storing capacity element of a stacked structure.

Incidentally, in all the Figures for describing the embodiments, partshaving identical functions are designated at common reference numerals,and their repeated descriptions will be omitted.

(Embodiment I)

A resin-sealed type semiconductor device for sealing a DRAM according tothe embodiment I of the present invention will be described withreference to FIG. 2 (of partially sectional, perspective view).

As shown in FIG. 2, the DRAM (of a semiconductor pellet) 1 is sealed byan SOJ (Small Out-line J-bend) type resin-sealed type semiconductordevice 2. The DRAM 1 is made to have a large capacity of 16 Mbits!×1bit! and a rectangular top plan size of 16.48 mm!×8.54 mm!. This DRAM 1is sealed by the resin-sealed type semiconductor device 2 of 400 mil!.

The aforementioned DRAM 1 has its principal surface arranged mainly withmemory cell arrays and peripheral circuits. Each of the memory cellarrays is arranged, as will be described in detail, with a matrix shapeof a plurality memory cells (or storage elements) for storing aninformation of 1 bit!. The aforementioned peripheral circuits arecomposed of direct peripheral circuits and indirect peripheral circuits.The direct peripheral circuits are circuits for directly controlling theinformation writing operations and the information reading operations ofthe memory cells. These direct peripheral circuits include row addressdecoder circuits, column address decoder circuits and sense amplifiercircuits. The indirect peripheral circuits are circuits for indirectlycontrolling the operations of the aforementioned direct peripheralcircuits. These indirect peripheral circuits include clock signalgenerators and buffer circuits.

The principal surface of the aforementioned DRAM 1, i.e., the surfacearranged with the aforementioned memory cell arrays and peripheralcircuits is arranged with inner leads 3A. Between the DRAM 1 and theinner leads 3A, there is sandwiched an insulating film 4. Thisinsulating film 4 is made of a polyimide resin film, for example. Theindividual surfaces of the insulating film 4 at the sides of the DRAM 1and the inner leads inner leads 3A are formed with adhesive layers(although not shown). This adhesive layer is made of a polyetheramide-imide resin or an epoxy resin, for example. The resin-sealed typesemiconductor device 2 of this type adopts the LOC (i.e., Lead On Chip)structure in which the inner leads 3A are arranged over the DRAM 1. Theresin-sealed type semiconductor device 2 thus adopting the LOC structurecan arrange the inner leads 3A freely without being regulated by theshape of the DRAM 1, so that the DRAM 1 having a large size can besealed to a more extent corresponding to that arrangement. In otherwords, the resin-sealed type semiconductor device 2 adopting the LOCstructure can have its sealed size suppressed, even if the size of theDRAM 1 is enlarged according to the large capacity, so that thepackaging density can be enhanced.

The aforementioned inner leads 3A have their oneside ends integratedwith outer leads 3B. These outer leads 3B have their individually fedsignals and numerals specified on the basis of the standardspecifications. In FIG. 2, the nearest lefthand one is the firstterminal, and the nearest righthand one is the fourteenth terminal. Theremotest righthand one (as numbered at the corresponding one of theinner leads 3A) is the fifteenth terminal, and the remotest lefthand oneis the twenty eighth terminal. In other words, this resin-sealed typesemiconductor device 2 is composed of totally twenty four terminals,i.e., the first to sixth terminals, ninth to fourteenth terminals, thefifteenth to twentieth terminals and twenty third to twenty eighthterminals.

The aforementioned first terminal is one for the power source voltageVcc. This power source voltage Vcc is an operating voltage of 5 V! ofthe circuit, for example. The second terminal is a data input signalterminal (D); the third terminal is a free terminal; the fourth terminalis a write enable signal terminal (W); the fifth terminal is a rowaddress strobe signal terminal (RE); and the sixth terminal is anaddress signal terminal (A₁₁).

The ninth terminal is an address signal terminal (A₁₀); the tenthterminal is an address signal terminal (A₀); the eleventh terminal is anaddress signal terminal (A₁); the twelfth terminal is an address signalterminal (A₂); and the thirteenth terminal is an address signal terminal(A₃). The fourteenth terminal is a power source voltage Vcc terminal.

The fifteenth terminal is a reference voltage Vss terminal. Thisreference voltage Vss is the reference voltage of 0 V! of the circuit,for example. The sixteenth terminal is an address signal terminal (A₄);the seventeenth terminal is an address signal terminal (A₅); theeighteenth terminal is an address signal terminal (A₆); the nineteenthterminal is an address signal terminal (A₇); and twentieth terminal isan address signal terminal (A₈).

The twenty third terminal is an address signal terminal (A₉); the twentyfifth terminal is a column address strobe signal terminal (CE); and thetwenty sixth terminal is a free terminal; and twenty seventh terminal isa data output signal terminal. The twenty eight terminal is a referencevoltage Vss terminal.

The other ends of the aforementioned inner leads 3A are extended acrossthe individual longer sides of the rectangle of the DRAM 1 to the centerof the DRAM 1. The other ends of the inner leads 3A have their leadingends are connected through bonding wires 5 with external terminals (orbonding pads) BP arranged at the center of the DRAM 1. The bonding wires5 are made of aluminum (Al) wires. On the other hand, the bonding wires5 to be used may be made of coated wires which are made by coating metalwires such as gold (Au) or copper (Cu) wires with an insulating resin.The bonding wires 5 are bonded by the bonding method using theultrasonic vibrations together with the hot contact molding.

Of the aforementioned inner leads 3A, the individual inner leads 3A ofthe fourteenth terminal are made integral and extended in the centralportion of the DRAM 1 in parallel with the longer sides of the same.Likewise, the respective inner leads (Vss) 3A of the fifteenth terminaland twenty eighth terminal are made integral and extended in the centralportion of the DRAM 1 in parallel with the longer sides of the same. Theinner leads (Vcc) 3A and inner leads (Vss) 3A are extended in parallelwithin the regions which are defined by the leading ends of the otherends of the remaining inner leads 3A. Those inner leads (Vcc) 3A andinner leads (Vss) 3A are individually enabled to supply the power supplyvoltage Vcc and the reference voltage Vss no matter what position of theprincipal surface of the DRAM 1 they might be disposed in. In otherwords, the resin-sealed type semiconductor device 2 is constructed toabsorb the power source noises easily thereby to increase the operatingspeed of the DRAM 1.

The rectangle of this DRAM 1 has its shorter sides equipped with pelletsupporting leads 3C.

The inner leads 3A, outer leads 3B and pellet supporting leads 3C thusfar described are individually cut from the lead frame and molded. Thislead frame is made of a Fe--Ni (having a Ni content of 42 or 50 %!, forexample) alloy or Cu, for example.

The DRAM 1, bonding wires 5, inner leads 3A and pellet supporting leads3C thus far described are sealed with a resin-sealing portion 6. Thisresin-sealing portion 6 is made of an epoxy resin to which are added aphenol curing agent, silicone rubber and a filler. The silicon rubberhas an action to drop the coefficient of thermal expansion of the epoxyresin. The filler is made of silicon oxide balls having an action todrop the coefficient of thermal expansion similarly.

Next, FIG. 3 shows a schematic structure of the DRAM 1 which is sealedwith the aforementioned resin-sealed type semiconductor device 2.

As shown in FIG. 3, the DRAM 1 is arranged substantially all over itssurface with a memory cell array (MA) 11. The DRAM 1 of the presentembodiment is roughly divided into four memory cell arrays 11A to 11C,although not limited thereto. In FIG. 3, the two memory cell arrays 11Aand 11B are arranged over the DRAM 1, and the two memory cell arrays 11Cand 11D are arranged under the same. Each of these four-divided memorycell arrays 11A to 11D is further divided into sixteen memory cellarrays (MA) 11E. In other words, the DRAM 1 is arranged sixty fourmemory cell arrays 11E. Each of the sixty four memory cell arrays 11E ismade to have a capacity of 256 Kbits!.

Between every two of the sixteen memory cell arrays 11E of theaforementioned DRAM 1, there is interposed a sense amplifier circuit(SA) 13. This sense amplifier circuit 13 is composed of complementaryMISFETs (i.e., CMOSes). A column address decoder circuit (i.e., YDEC) 12is arranged at the lower one end of each of the two 11A and 11B of thefour divided memory cell arrays of the DRAM 1. Likewise, a columnaddress decoder circuit. (i.e., YDEC) 12 is arranged at the upper oneend of each of the two memory cell arrays 11C and 11D.

Word driver circuits (WD) 14, row address decoder circuits (XDEC) 15 andunit mat control circuits 16 20 are individually arranged in the recitedorder from the lefthand to the righthand at one end of the righthandside of each of the two 11A and 11C of the four divided memory cellarrays of the aforementioned DRAM 1. Word driver circuits 14, rowaddress decoder circuits 15 and unit mat control circuits 16 areindividually arranged in the recited order from the righthand to thelefthand at one end of the righthand side of each of the two memory cellarrays 11B and 11D.

Each of the aforementioned sense amplifier circuits 13, column addressdecoder circuits 12, word driver circuits 14 and row address decodercircuits 15 constitutes a direct one of the peripheral circuits of theDRAM 1. This direct peripheral circuit is one for directly controllingthe memory cells which are arranged in the finely divided memory cellarrays 11E of the memory cell array 11.

Between the two 11A and 11B and the two 11C and 11D of the four dividedmemory cells of the DRAM 1, respectively, there are interposedperipheral circuits 17 and the external terminals BP. As the peripheralcircuits 17, there are arranged an output buffer circuit 1702, asubstrate potential generator circuit (i.e., V_(BB) generator circuit)1703 and a power source circuit 1704. Four sets of totally sixteen mainamplifier circuits 1701 are arranged. Totally four output buffercircuits 1702 are arranged.

The aforementioned external terminals BP are arranged at the centralportion of the DRAM 1 because the aforementioned resin-sealed typesemiconductor device 2 is constructed to have the LOC structure so thatthe inner leads 3A are extended to the central portion of the DRAM 1.The external terminals BP are so arranged within the regions defined bythe memory cell arrays 11A and 11C, and 11B and 11D that they aredirected from the upper end to the lower end of the DRAM 1. Thedescriptions of the signals to be fed to the external terminals BP willbe omitted here because they have been accomplished in the resin-sealedtype semiconductor device 2 shown in FIG. 2. Since the inner leads 3Afed with the reference voltage (Vss) and the power source voltage (Vcc)are arranged from the upper end to the lower end of the surface of theDRAM 1, this DRAM 1 is arranged in its extending direction with aplurality of external terminals BP for the reference voltage (Vss) andthe power source voltage (Vcc). In other words, the DRAM 1 is enabled tosupply the respective power sources of the reference voltage (Vss) andthe power source voltage (Vcc). The data input signal (D), the dataoutput signal (Q), the address signals (A₀ to A₁₁), the clock signalsand control signals are concentratedly arranged at the central portionof the DRAM 1.

Between the two 11A and 11C and the two 11B and 11D of the four dividedmemory cells of the DRAM 1, respectively, there are interposedperipheral circuits 18. The lefthand side peripheral circuits 18 includea row address strobe (RE) circuit 1801, a write enable (W) circuit 1802,a data input buffer circuit 1803, a VCC limiter circuit 1804, anX-address driver circuit (or a logical step) 1805, an X-ray redundancycircuit 1806 and an X-address buffer circuit 1807. The righthand sideperipheral circuits include a column address strobe (CE) circuit 1808, atest circuit 1809, a VDL limiter circuit 1810, a Y-address drivercircuit (or a logical step) 1811, a Y-redundancy circuit 1812 and aY-address buffer circuit 1813. The central peripheral circuits 18include a Y-address driver circuit (or a drive step) 1814, an X-addressdriver circuit (or a drive step) 1815 and a mat selection signal circuit(or a drive step) 1816.

The aforementioned peripheral circuits 17 and 18 (and 16) are used asthe indirect peripheral circuits of the DRAM 1.

Next, the essential portions of the sixteen divided memory cell arrays11E of the aforementioned DRAM 1 and the essential portions of theirperipheral circuits will be described with reference to FIG. 4(presenting an essential equivalent circuit diagram).

As shown in FIG. 4, the aforementioned DRAM 1 is constructed to have thefolded bit line structure (or the double-point intersection structure).In each of the sixteen divided memory cell arrays 11 of the DRAM 1,there are arranged in a matrix shape a plurality of memory cells M.These memory cells M are arranged at the intersections betweencomplementary data lines (or complementary bit lines) DL and DL and wordlines WL. The complementary data lines DL are extended in the rowdirection of FIG. 4 and arranged in plurality in the column direction.The word lines WL are extended in the column direction and arranged inplurality in the row direction. With the complementary data lines DLextended in the column direction, there are individually connected senseamplifier circuits Sa of the shared sense type, precharge circuits DPand input/output signal selector circuits VO. The aforementioned wordlines WL are connected with the row address decoder circuits (XDEC) 15through word driver circuits (WD) 14, as shown in FIG. 3. Although notshown in FIG. 4, shunting word lines WL extended in the column directionare arranged along the aforementioned word lines WL. The shunting wordlines WL are shorted at predetermined portions (at every a predeterminednumber of memory cells, for example) with the word lines WL to reducethe specific resistances of the word lines WL.

Each of the aforementioned memory cells M is constructed of a seriescircuit composed of a memory cell selecting MISFET Qs and theinformation storing information storing capacity element C. The memorycell selecting MISFET Qs is made to have an n-channel. This memory cellselecting MISFET Qs has its one semiconductor region connected with theaforementioned complementary data line DL. The other semiconductorregion is connected with one electrode (or a lower electrode layer) ofthe information storing capacity element C. The gate electrode isconnected with the word line WL. The other electrode of the informationstoring capacity element C is connected with a lower power sourcevoltage of 1/2• Vcc. The aforementioned DRAM 1 uses the aforementionedpower source voltage Vcc, i.e., 5 V! as the operating voltage of theinput step circuit and the output step circuit to be used as theinterface with an external unit. A lower power source voltage Vcc, e.g.,3.3 V! than the power source voltage Vcc is used as the operatingvoltage of the internal circuits of the DRAM 1 e.g., the memory cellarray 11, the direct peripheral circuits (2, 13, 14 and 15) and theindirect peripheral circuits (16, 17 and 18). The lower power sourcevoltage Vcc can reduce the amount of charge and discharge of thecomplementary data lines DL especially in the information writingoperations and the information reading operations so that the powerconsumption of the DRAM 1 can be reduced. Therefore, the aforementionedlower power source voltage 1/2• Vcc takes an intermediate value of about1.65 V! between the lower power source voltage Vcc and the referencevoltage Vss.

The aforementioned precharge circuit DP is composed of: two prechargingMISFETs having their gate electrodes connected with a precharge signalline .o slashed. pc; and a shorting MISFET having its gate electrodelikewise connected with the precharge signal line .o slashed. pc. Eachprecharging MISFET has its one semiconductor region connected with thecomplementary data lines DL and its other semiconductor region connectedwith a common source line (or the reference voltage Vss) PN. Theshorting MISFET has its individual semiconductor regions connected withthe complementary data lines DL. The precharging MISFETs and theshorting MISFET are constructed to have the n-channel.

The sense amplifier circuits Sa is composed of two n-channel MISFETs Qnand two p-channel MISFETs Qp. Each of the n-channel MISFETs Qn of thesense amplifier circuits-Sa has its one semiconductor region connectedwith the complementary data lines DL and its other semiconductor regionconnected with the common source lines (at the reference potential Vss)PN. The n-cahnnel MISFETs Qn have their individual gate electrodesintersecting each other and connected with the other of thecomplementary data lines DL, one of which is connected with thesemiconductor region of one of them. Each of the p-channel MISFETs Qp ofthe sense amplifier Sa has its one semiconductor region connected withthe complementary data lines DL and its other semiconductor regionconnected with a common source line (at Vcc of 3.3 V!) PP. The p-channelMISFETs Qp have their individual gate electrodes intersecting each otherand connected with the other of the complementary data lines DL, one ofwhich is connected with the semiconductor region of one of them.

The input/output signal selector circuit VO is composed of n-channelinput/output selecting MISFETs (or column switches). These input/outputselecting MISFETs are arranged at every data lines of the complementarydata lines DL. Each of the input/output selecting MISFET has its onesemiconductor region connected with the complementary data lines DL andits other semiconductor region connected with any of complementaryinput/output signal lines I/O. With the gate electrode of theinput/output selecting MISFET, there is connected a column select signalline YSL. This column select signal line YSL is connected with thecolumn address decoder circuits 12.

The aforementioned sense amplifier circuit 13 is arranged with the matselecting MISFETs between the complementary data lines DL of the uppermemory cell arrays 11E and the sense amplifiers Sa and the complementarydata lines DL of the lower memory cell arrays 11E and the input/outputsignal selector circuits. Those mat selecting MISFETs are constructed tohave the n-channel and to be controlled by mat selection signals SHL andSHR. In the vicinity of the aforementioned sense amplifier circuits 13,the memory cell arrays 11E are arranged with dummy cells DS at theintersections between the complementary data lines DL and dummy wordlines DWL. These dummy cells DS are composed of n-cahnnel MISFETs.

Moreover, the word lines WL of the aforementioned memory cell array 11Eare arranged with clearing MISFETs at their side opposite to the worddriver circuits 14. The clearing MISFETs are controlled by clear signalsWLC.

Next, the specific structures of the elements composing the memory cellsM and the peripheral circuits (e.g., the sense amplifier circuits or thedecoder circuits) of the aforementioned DRAM 1 will be described in thefollowing. The structure of the memory cell array 11E is shown in FIG. 5(in a partial top plan view). The sectional structures of the memorycell array 11E and the elements of the peripheral circuits are shown inFIG. 1 (in a partial section). Incidentally, the sectional structure ofthe memory cell M, as shown at the lefthand side of FIG. 1, presents thesectional structure of the portion taken from line I--I of FIG. 5. Onthe other hand, the righthand side of FIG. 1 presents the sectionalstructure of the complementary MISFET (i.e., CMOS) composing theperipheral circuits.

As shown in FIGS. 1 and 5, the DRAM 1 is constructed of a p⁻ -typesemiconductor substrate 20 made of single crystalline silicon. This p⁻-type semiconductor substrate 20 uses the (100) crystal plane as anelement forming plane to have a resistance of about 10 Ω/cm!, forexample. The principal surface of a portion of the p⁻ -typesemiconductor substrate 20 is not doped with an n-type impurity morethan about 10¹⁵ atom/cm² ! by the ion implantation. The partial regionis at least that of the memory cell array 11E. The introduction of theaforementioned n-type impurity will cause many crystal defects to leakthe charges of information so that the area to be doped with theimpurity is partially limited. In order to reduce the contamination witha heavy metal such as Fe, therefore, the DRAM 1 used in the presentembodiment has a getter ring layer in a deep region of the p⁻ -typesemiconductor substrate 20.

This p⁻ -type semiconductor substrate 20 is formed with a p⁻ -type wellregion 22 in the principal surface of the regions to be formed with thememory cells M (e.g., the memory cell arrays 11E) and the n-channelMISFET Qn. On the other hand, the p⁻ -type semiconductor substrate 20 isformed with an n⁻ -type well region 21 in the principal surface of theregions to be formed with the p-channel MISFETs Qp. In other words, theDRAM 1 of the present embodiment is constructed to have the twin wellstructure. The p⁻ -type well region 22 is formed in a self-alignmentwith the n⁻ -type well region 21.

The individual regions of those well regions 21 and 22 to be formed withthe semiconductor elements are formed over their intervening regions(i.e., inactive regions) with an element separating insulating film(i.e., a field insulating film) 23. The principal surface-portions ofthe p⁻ -type well region 22 to be formed with the memory cell arrays 11Eare formed with p-type channel stopper regions 25A below the elementseparating insulating film 23 (i.e., in the inactive regions). Since theparasitic MOSes using the element separating insulating film 23 as thegate insulating film are liable to be inverted to the n-type, thechannel stopper regions are formed in at least the principal surfaceportions of the p⁻ -type well regions 22. The p-type channel stopperregions 25A are made to have a higher impurity concentration than thoseof the p⁻ -type semiconductor substrate 20 and the p⁻ -type well region22.

The regions of the memory cell arrays 11E to be formed with the memorycells M are formed with p-type semiconductor regions 25B in theprincipal surface of the p⁻ -type well regions 22. The p-typesemiconductor regions 25B are formed substantially all over the surfaceof the active regions of the memory cell arrays 11E. The p-typesemiconductor regions 25B are formed at the step shared with theaforementioned p-type channel stopper regions 25A. The p-typesemiconductor regions 25B and the p-type channel stopper regions 25A areformed, as will be described in detail hereinafter, by doping theindividual principal surface portions of the active and inactive regionsof the memory cell arrays 11E of the p⁻ -type well regions 22 with animpurity, after forming the aforementioned element separating insulatingfilm 23, and by activating the impurity. This impurity to be used is B,for example, and is introduced by the ion implantation of high energy.The principal surface portions of the inactive regions of the p⁻ -typewell regions 22 are passed through the element separating insulatingfilm 23 so that they may be doped with the impurity. The principalsurface portions of the active regions (to form the memory cells M) aredoped with the aforementioned impurity in positions which are located sodeep from the principle surface as to correspond to the thickness of theaforementioned element separating insulating film 23.

The p-type channel stopper regions 25A thus constructed are formed within self-alignment with the element separating insulating film 23 andafter a heat treatment for forming the element separating insulatingfilm 23, as will be described hereinafter. This makes it possible toreduce the amount of diffusion of the p-type impurity forming the p-typechannel stopper regions 25A into the active regions. This reduction inthe diffusion amount of the p-type impurity can lead to a reduction inthe narrow channel effect of the memory selecting MISFETs Qs of thememory cells M. On the other hand, the p-type semiconductor regions 25Bare formed below the memory cells M to act as potential barrier regionsagainst the minority carriers so that they can raise the resistance tothe α-ray soft errors. Moreover, the p-type semiconductor regions 25Bcan increases the impurity concentration of the principal surface of thep⁻ -type well regions 22 to a slightly higher value to raise thethreshold voltage of the memory cell selecting MISFETs Qs so that noerroneous conduction will arise even if noises are caused in the wordlines WL or the line in nonselected states. Furthermore, the p-typesemiconductor regions 25B can increase the pn junction capacitor, whichis formed in semiconductor regions 29 at the side of the memory cellselecting MISFETs Qs to be connected with the electrodes of theinformation storing capacity elements C so that they can increase thecharge storing amount of the information storing capacity elements C.

The memory cell selecting MISFET Qs of the aforementioned memory cells Mare formed in the principal surface portions of the p⁻ -type wellregions 22, as shown in FIGS. 1, 5 and 6 (presenting top plan views ofthe essential portion at predetermined fabrication steps). As a matterof fact, the memory cell selecting MISFETs Qs are formed in theprincipal surface portions of the p⁻ -type well regions 22, which aresurrounded by the p-type semiconductor regions 25B to have a slightlyhigher impurity concentration. The memory cell selecting MISFETs Qs areformed in the regions which are defined by the element separatinginsulating film 23 and the p-type channel stopper regions 25A. Thememory cell selecting MISFETs Qs are constructed mainly of the p⁻ -typewell regions 22, gate insulating film 26, gate electrodes 27 and a pairof semiconductor regions 29, i.e., source regions and drain regions.

The aforementioned p⁻ -type well regions 22 are used as channel formingregions. The gate insulating film 26 are formed of the silicon oxidefilm which is prepared by oxidizing the principal surfaces of the p⁻-type well regions 22. In case, on the other hand, the insulatingwithstand voltage is to be retained as the gate insulating film 26 arethinned, this gate insulating film 26 may be formed of a composite filmwhich is prepared by laminating silicon oxide films and silicon nitridefilms sequentially.

The gate electrodes 27 are formed over the gate insulating film 26. Thegate electrodes 27 are formed of polycrystalline silicon films, whichare deposited by the CVD method, for example, to have a thickness ofabout 200 to 300 nm!. These polycrystalline silicon films are doped withan n-type impurity (P or As) for reducing the resistance. Moreover, thegate electrodes 27 may be made of a single layer of a transition metal(e.g., a metal of high melting point such as Mo, Ti, Ta or W) film orits silicide (MoSi₂, TiSi₂ TaSi₂ or WSi₂) film. Moreover, the gateelectrodes 27 may be made of a composite film which is prepared bylaminating the aforementioned transition-metal film or its silicidefilm.

The gate electrodes 27 are formed, as shown in FIGS. 5 and 6, integrallywith the word lines (WL) 27 extending in the column direction. In otherwords, the gate electrodes 27 and the word lines 27 are formed of acommon conductive layer. The word lines 27 are constructed to connectthe individual gate electrodes 27 of the memory cell selecting MISFETsQs of the plural memory cells M arranged in the column direction.

As shown in FIG. 6, the gate length of the gate electrodes 27 of thememory cell selecting MISFETs Qs is made longer than the width of theword lines 27. For example, the gate electrodes 27 have a gate length of0.7 μm! and a width of 0.5 μm!. In short, the memory cell selectingMISFETs Qs are enabled to retain the effective gate (or channel) lengththereby to reduce the short channel effect. On the other hand, the wordlines 27 are constructed to minimize the gap inbetween thereby to reducethe area of the memory cells M so that they may improve the degree ofintegration. Those word lines 27 reduce the resistance with shuntingword lines (WL) 55, as will be described hereinafter, so that theiroperating speeds such as the information writing operations or theinformation reading operations are not dropped even if the width isreduced. Incidentally in the present embodiment, the DRAM 1 adopts theso-called "0.5 μm! fabrication process" having minimum processing sizeof 0.5 μm!.

The semiconductor regions 29 are formed to have a lower impurityconcentration than that of n⁺ -type semiconductor region 32 of theMISFETs Qn composing the peripheral circuits. More specifically, thesemiconductor regions 29 are formed at a low impurity concentration of1×10¹⁴ atoms/cm² ! by the ion implantation. In other words, thesemiconductor regions 29 are enabled to reduce the occurrence of thecrystal defects to be caused as a result of the introduction of theimpurity and to restore the crystal defects sufficiently by a heattreatment after the impurity introduction. Since the semiconductorregions 29 have a small leakage current amount at their pn junctionswith the p⁻ -type well regions 22, the information charges stored in theinformation storing capacity elements C can be stably held.

Since the semiconductor regions 29 are formed in a self-alingment withthe gate electrodes 27 and made to have a lower impurity concentrationat their side to be formed with the channels, they construct the memorycell selecting MISFETs Qs having the LDD (Lightly Doped Drain)structure.

On the other hand, one-side (at the side to be connected withcomplementary data lines 50) semiconductor regions 29 of the memory cellselecting MISFETs Qs are diffused, in the regions specifiedlater-described connecting holes (40A), with an n-type impurity, whichis introduced into polycrystalline silicon film (50A)below thecomplementary data lines (50), so that they have a slightly higherimpurity concentration. Since the n-type impurity to be introduced intothe n-type semiconductor regions can connect the n-type semiconductorregions 29 and the complementary data lines (50) ohmically, it canreduce the resistances of the connected portions. Moreover, the n-typeimpurity forms the n-type semiconductor regions so as to prevent thecomplementary data lines (50) and the p⁻ -type well regions 22 frombeing shorted, even in case a masking misregistration is caused at thefabrication step between the semiconductor regions 29 and theaforementioned connecting holes (40A) to superpose the connecting holes(40A) and the element separating insulating film 23 so that the p⁻ -typewell regions 22 have their principal surfaces exposed to the inside ofthe connecting holes (40A).

The other-side (at the side to be connected with the information storingcapacity elements C) semiconductor regions 29 of the memory cellselecting MISFETs Qs are diffused with the n-type impurity, which isintroduced into a lower electrode layer (35) of the information storingcapacity elements C, so that the impurity concentration is made slightlyhigher. The n-type impurity to be introduced into the semiconductorregions 29 can connect the semiconductor regions 29 and the lowerelectrode layer (35) ohmically to reduce the resistances of theconnected portions. Moreover, this n-type impurity can increase theimpurity concentration of the semiconductor regions 29 to augment thecapacity of the pn junctions, which are formed of the semiconductorregions 29 and the p⁻ -type well regions 22, so that it can augment thecharge store amount of the information storing capacity elements C.

The gate electrodes 27 of the aforementioned memory cell selectingMISFET Qs are formed thereover with a insulating film 28, and the gateelectrodes 27 and the insulating film 28 are formed at their individualside walls with side wall spacers 31. The insulating film 28 are mademainly to separate the gate electrodes 27 and the individual electrodes(especially 35) of the information storing capacity elements C formedover the former. The side wall spacers 31 are so formed in the regionsformed with the memory cells M and in a self-alignment with the gateelectrodes 27 of the memory cell selecting MISFETs Qs as to connect theother semiconductor regions 29 and the lower electrode layer (35) of theinformation storing capacity elements C. Moreover, the side wall spacers31 are constructed to give the CMOSes the LDD structure in the regionsformed with the peripheral circuits. The aforementioned insulating film28 and side wall spacers 31 are formed of a silicon oxide film, which isdeposited by the CVD method using inorganic silane gases and nitrogenoxide gases as its source gases, although their fabrication method willbe described hereinafter. The silicon oxide film thus formed has ahigher step coverage at the underlying stepped portions and a smallerfilm shrinkage than those of the silicon oxide film which is deposed bythe CVD method using organic silane gases as its source gases. In otherwords, the insulating film 28 and side wall spacers 31 formed by thismethod can reduce their separations due to the film shrinkage to preventthe aforementioned gate electrodes 27 and the remaining conducting layersuch as the lower electrode layer 35 from being shorted.

The information storing capacity elements C of the aforementioned memorycells M are constructed mainly by laminating the lower electrode layer35, a dielectric film 36 and upper electrode layer 37 sequentially, asshown in FIGS. 1, 5 and 7 (presenting partial top plan views atpredetermined fabrication. steps). The information storing capacityelements C are constructed to have the so-called "stacked structure (oflaminated type: STC)".

The lower electrode layer 35 of the information storing capacityelements C of this stacked structure is partially (at its centralportion) with the other semiconductor regions 29 of the memory cellselecting MISFETs Qs. These connections are accomplished through bothconnecting holes 33A, which are formed in an inter-layer insulating film33, and the connecting holes 34 which are defined by the side wallspacers 31 and 33B. The opening size of the connecting holes 34 in therow direction is specified by both the gaps of the gate electrodes 27 ofthe memory selecting MISFETs Qs and the word lines 27 adjoining theformer and the individual film thicknesses of the side wall spacers 31and 33B. The difference between the opening size of the connecting holes33A and the connecting holes 34 is made larger than at least thatcorresponding to the masking allowance at the fabrication steps. Theother (or peripheral) portions of the lower electrode layer 35 areextended to above the gate electrodes 27 and the word lines 27.

The aforementioned inter-layer insulating film 33 is formed of aninsulating film like that of the underlying insulating film 28 and sidewall spacers 31. In other words, the inter-layer insulating film 33 ismade of the silicon oxide film which is deposited by the CVD methodusing the inorganic silane gases and the nitrogen oxide gases as itssource gases.

The aforementioned lower electrode layer 35 is made of thepolycrystalline silicon film deposited by the CVD method, for example,and this polycrystalline silicon film is highly doped with an n-typeimpurity (e.g., As or P) for reducing the resistance. The lowerelectrode layer 35 is made to increase the area of the side walls of itssurface and accordingly the charge storage capacity of the informationstoring capacity elements C having the stacked structure. The lowerelectrode layer 35 is formed to have a film thickness equal to or largerthan the half size of the opening size in the gate length direction sothat its surface may be flattened. For example, the lower electrodelayer 35 is formed to have a relatively large film thickness of about400 to 600 nm!. The lower electrode layer 35 is constructed to have arectangular top plan shape elongated in the row direction of thecomplementary data lines 50.

The dielectric film 36 is basically constructed to have a two-layeredstructure, in which there are laminated a silicon nitride film 36Adeposited by the CVD method over (or on the surface of) the lowerelectrode layer (of the polycrystalline silicon film) 35 and a siliconoxide film 36B formed by oxidizing the silicon nitride film 36A under ahigh pressure. As a matter of fact, the dielectric film 36 isconstructed to have a three-layered structure, in which a naturalsilicon oxide film (although not shown because it is thinner than 5nm!), the silicon nitride film 36A and the silicon oxide film 36B aresequentially laminated, because the natural silicon oxide film is formedon the surface of the polycrystalline silicon film of the lowerelectrode layer 35. Since the silicon nitride film 36A of theaforementioned dielectric film 36 is deposited by the CVD method, it canbe formed under process conditions independent of the underlying layerwith being influenced neither the crystal state nor the stepped shape ofthe underlying polycrystalline silicon film (i.e., the lower electrodelayer 35). In short, the silicon nitride film 36A has a higherinsulating breakdown voltage and a smaller number of defects per unitarea than those of the silicon oxide film, which is formed by oxidizingthe surface of the polycrystalline silicon film, and accordingly a verylittle leakage current. Moreover, the silicon nitride film 36A isfeatured by its a higher dielectric constant than that of the siliconoxide film. The silicon oxide film 36B can be formed of a very excellentfilm to improve the aforementioned characteristics of the siliconnitride film 36A better. Although will be described in more detailhereinafter, moreover,r the silicon oxide film 36B is oxidized under ahigh pressure (e.g., 1.5 to 10 tolls!) so that it can be formed for ashorter oxidization or heat treatment time than that of the oxidizationunder a normal pressure.

The dielectric film 36 is formed on the upper surface and side walls ofthe lower electrode layer 35 to take an area in the vertical directionby making use of the side wall portions of the lower electrode layer 35.This increase of the area of the dielectric film 36 can improve thecharge storage of the information storing elements C having the stackedstructure. The top plan shape of this dielectric film 36 is specified bythat of the upper electrode layer 37 to have a substantially identicalshape to that of the upper electrode layer 37.

This upper electrode layer 37 is so formed over the lower electrodelayer 35 as to cover it through the dielectric film 36. The upperelectrode layer 37 is made integral with the upper electrode layer 37 ofthe information storing capacity elements C of the stacked structure ofthe adjoining other memory cells M. The upper electrode layer 37 is fedwith the lower power source voltage of 1/2• Vcc. The upper electrodelayer 37 is formed of the polycrystalline silicon film which isdeposited by the CVD method, for example, and this polycrystallinesilicon film is doped with an n-type impurity for reducing theresistance. The upper electrode layer 37 is made thinner than theaforementioned lower electrode layer 35. The upper electrode layer 37 isformed on its surface with an insulating film 38. This insulating film38 is formed when the stepped portion of the underlying surface leftunetched when the upper electrode layer 37 is treated is removed, aswill be described hereinafter.

The dielectric film 36 of the information storing capacity elements Chaving the aforementioned stacked structure is formed over theinter-layer insulating film 33 at the regions other than the lowerelectrode layer 35. The inter-layer insulating film 33 is formed of thesilicon oxide film which is deposited by the CVD method using theinorganic silane gases and the nitrogen oxide gases as its source gases,as has been described hereinbefore. In other words, the dielectric film36, especially its underlying silicon nitride film 36A contacts with theinter-layer insulating film 33 having less film shrinkage so that theinformation storing capacity elements C of this stacked structure canprevent any breakage due to the stress of the dielectric film 36.

The aforementioned memory cell M are connected with another memory cellwhich is adjacent in the row direction, as shown in FIGS. 1, 5, 6 and 7.In other words, the two memory cells M adjoining in the row directionhave one of their individual memory cell selecting MISFETs Qs integratedat its n-type semiconductor regions to form an inverted pattern at thoseportions. These two memory cells M are arranged in plurality in thecolumn directions and at an offset of a half pitch in the row directionfrom the other two memory cells M which are adjacent thereto in the rowdirection.

With one n-type semiconductor regions 29 of the memory cell selectingMISFETs Qs of the memory cells M, as shown in FIGS. 1 and 5, there areconnected the complementary data lines (DL) 50. These complementary datalines 50 are connected with the n-type semiconductor regions 29 throughthe connecting holes 40A which are formed in the interlayer insulatingfilms 33 and 40.

These interlayer insulating film 40 is formed of an silicon oxide filmwhich is deposited by the CVD method using inorganic silane gases andnitrogen oxide gases as its source gases, for example. The informationstoring capacity elements C having the aforementioned stacked structureare highly stepped partly because the lower electrode layer 35, thedielectric film 36 and the upper electrode layer 37 are sequentiallysuperposed and partly because the lower electrode layer 35 is madethick. Thus, the interlayer insulating film 40 has its surfaceflattened. Specifically, the interlayer insulating film 40 has itsstepped surface shape grown to an extent corresponding to the thicknessof the lower electrode layer 35 so that its surface is flattened byburying the inter-layer insulating film 40 between the aforementionedlower electrode layer 35 and another adjacent lower electrode layer 35.The regions of the minimum gap between the lower electrode layers 35 ofthe information storing capacity elements C of the stacked structure ofthe adjoining memory cells M are formed into a large stepped shapehaving an aspect ratio of 1 or more. The minimum gap between the lowerelectrode layers 35 is about 0.5 μm!. Between these lower electrodelayers 35, there are interposed the dielectric film 36 and the upperelectrode layer 37. Thus, the interlayer insulating film 40 is made tohave one half or more thickness of the minimum gap between the lowerelectrode layers 35 which interpose the dielectric film 36 and the upperelectrode layer 37 inbetween. Moreover, the interlayer insulating film40 is made so thick as to retain the insulating breakdown voltage andreduce the parasitic capacity. For example, the interlayer insulatingfilm 40 is made to have a thickness of 250 to 350 nm!.

The complementary data lines 50 are made of a composite film having atwo-layered structure, in which the polycrystalline silicon film SOA andthe transition-metal silicide film 50B are sequentially laminated. Thelower polycrystalline silicon film 50A is deposited by the CVD method tohave a thickness of about 100 to 150 nm!, for example. The lowerpolycrystalline silicon film 50A is doped with an n-type impurity suchas P for reducing the resistance. The lower polycrystalline silicon filmSOA has an excellent step coverage at the underlying stepped portion sothat it can reduce the defects such as the disconnections. An uppertransition-metal silicide film 50B is deposited by the CVD (orsputtering method) to have a thickness of about 100 to 200 nm!, forexample. The upper transition-metal silicide film SOB can reduce theresistance of the complementary data lines 50 to increase the operatingspeeds such as the information writing operations and the informationreading operations. Moreover, the upper transition-metal silicide film50B has an excellent step coverage in the underlying stepped portion sothat it can reduce the defects such as the disconnections of thecomplementary data lines 50. The individual lower polycrystallinesilicon film 50A and upper transition-metal silicide film 50B of thecomplementary data lines 50 have resistances to heat and oxidation. Thecomplementary data lines 50 are made to have a winding width of about0.6 μm!.

In the DRAM 1 constructed of the series circuit which is composed of:the memory cell selecting MISFETs Qs having the complementary data lines50 connected with one of the n-type semiconductor regions 29; and theinformation storing capacity elements C of the stacked structurelaminated sequentially thereover with the lower electrode layer 35, thedielectric film 36 and the upper electrode layer 37, the aforementionedcomplementary data lines 50 formed of the composite film, in which thepolycrystalline silicon film 50A and transition-metal silicide film 50Bhaving the interlayer insulating film 40 interposed inbetween anddeposited by the CVD method are sequentially laminated, are formed overthe upper electrode layer 37 of the information storing capacityelements C of the aforementioned stacked structure, and the thickness ofthe interlayer insulating film 40 between the upper upper electrodelayer 37 and the complementary data lines 50 is larger than one half ofthe gap interposing the upper electrode layer 37 between the lowerelectrode layer 35 of the information storing capacity elements C of thestacked structure of the aforementioned memory cells M and the lowerelectrode layer 35 of the information storing capacity elements C of thestacked structure of other memory cells adjacent to the former lowerelectrode layer 35 with the minimum gap. Since, according to thisconstruction, the transition-metal silicide film SOB over theaforementioned complementary data lines 50 causes the mutual diffusionsof the impurity, the flattening of the underlying surface of thecomplementary data lines 50 cannot be promoted by effecting the flowusing the BPSG film or the PSG film as the interlayer insulating film40. By controlling the thickness of the inter-layer insulating film 40on the basis of the size of the gap between the lower electrode layers35 adjacent to each other at the aforementioned minimum gap, however,the gap between the lower electrode layers 35 can be buried with theinterlayer insulating film 40 to flatten the surface of the interlayerinsulating film 40. As a result, the shortening between thecomplementary data lines 50, which might otherwise be caused by theresidual left unetched at the stepped portions of the interlayerinsulating film 40 between the lower electrode layers 35 when in theworking of the complementary data lines 50, can be prevented to improvethe electrical reliability.

Over the complementary data lines 50, there are constructed columnselect signal lines (YSL) 52 through an interlayer insulating film 51.

This interlayer insulating film 51 is constructed, for example, of acomposite film of the two-layered structure, in which are sequentiallylaminated a silicon oxide film 51A deposited by the CVD method and aBPSG film 51B which is deposited by the CVD method. The lower siliconoxide film 51A is formed to prevent the B or P added to the upper BPSGfilm 51B from leaking to the lower layer. The lower silicon oxide film51A is formed of a silicon oxide film which is deposited by the CVDmethod using the inorganic silane gases and the nitrogen oxide gases asits source gases, for example. The lower silicon oxide film 51A isformed to have a thickness of about 100 to 200 nm!, for example. Theupper BPSG film 51B has its surface subjected to a flowing treatment sothat it may be flattened. The BPSG film 51B is formed to have athickness of about 250 to 350 nm!, for example.

The aforementioned column select signal lines 52 is made of atansition-metal film deposited by the sputtering method, for example,because it is deposited on the surface of the underlying interlayerinsulating film 51. This transition-metal film is made of a W film, forexample. The column select signal lines 52 are formed to have athickness of about 350 to 450 nm!, for example. Since these columnselect signal lines 52 are formed in an upper-layer different from theaforementioned complementary data lines 50, they are neither regulatedby the wiring pitch of the complementary data lines 50 nor avoid theconnected portions of the complementary data lines 50 and the memorycells M. In order words, the column select signal lines 52 can beextended wider than the wiring width of the complementary data lines 50and substantially straight so that they can reduce the resistance. Thecolumn select signal lines 52 are formed to have a wiring width of about2.0 μm!, for example.

Over the column select signal lines 52, there are constructed theshunting word lines (WL) 55 through an interlayer insulating film 53.The shunting word lines 55 are connected with the aforementioned wordlines (WL) 27 although not shown, in predetermined regions correspondingto the individual several tens to hundreds memory cells M. The wordlines 27 are divided into plurality in the extending direction in thememory cell arrays lE, and the shunting word lines 55 are connected withthe divided individual word lines 27. The shunting word lines 55 areenabled to reduce the resistance of the word lines 27 thereby toincrease the selecting speed of the memory cells M in the informationwriting operations and the information reading operations.

The aforementioned interlayer insulating film 53 is constructed, asshown in FIG. 1, of a three-layered structure made of a composite film,in which a silicon oxide film (e.g., a deposited type insulating film)53A, a silicon oxide film (e.g., an applied type insulating film) 53Band silicon oxide film (e.g., a deposited type insulating film) 53C aresequentially laminated. The silicon oxide film 53A under and the siliconoxide film 53C over the interlayer insulating film 53 are deposited bythe conformal plasma CVD (which will be shortly referred to as the"C-CVD") method using tetraethoxysilane (TEOS: Si(OC₂ H₅)₄) gases as itssource gases. The under silicon oxide film 53A and the upper siliconoxide film 53C thus deposited by the C-CVD method can be deposited atlow temperatures (not higher than about 400 ° C.!) to have a high stepcoverage. These lower silicon oxide film 53A and upper silicon oxidefilm 53C are formed to have thicknesses of about 250 to 350 nm!, forexample. The intermediate silicon oxide film 53B of the interlayerinsulating film 53 is formed of a silicon oxide film which is bakedafter having been applied by the SOG (Spin On Glass) method. Thisintermediate silicon oxide film 53B is formed to flatten the surface ofthe interlayer insulating film 53. The intermediate silicon oxide film53B is baked after the application and has its whole surface etcheduntil it is buried only in the recess of the stepped portion.Specifically, the intermediate silicon oxide film 53B is so etched offas will be described hereinafter, that it may not be left in thesurfaces of the inner walls of connecting holes 53d formed in theinterlayer insulating film 53. In other words, the intermediate siliconoxide film 53B is enabled to reduce the corrosion of the aluminum filmor its alloy film of the aforementioned shunting word lines 55 by thewater contained in the silicon oxide film 53B. This intermediate siliconoxide film 53B is applied to have a thickness of about 100 nm!, forexample.

The aforementioned shunting shunting word lines 55 are constructed of acomposite film in which the transition-metal nitride film (or thetransition-metal silicide film) 55A and the aluminum alloy film (or analuminum film) 55B are sequentially laminated.

The lower transition-metal nitride film 55A is made of a TiN film actingas a barrier, for example, in case Cu is added to the upper aluminumalloy film 55B. On the other hand, the lower transition-metal nitridefilm 55A is made of a TiN film, for example, in case Si is added to theupper aluminum alloy film 55B. In this case, moreover, the lowertransition-metal nitride film 55A is formed of a transition-metalsilicide film such as MoSi₂. This lower transition-metal nitride film55A is deposited by the sputtering method, for example, to have athickness of about 100 nm!. In case the TiN film is used as the lowertransition-metal nitride film 55A, it has a crystal orientation of(200), as will be described in detail hereinafter.

The upper aluminum alloy film 55B has additional contents of Cu and Si.The Cu is added at about 0.5 wt. %!, for example, to reduce themigration phenomena. The Si is added at about 1.5 wt. %!, for example,to reduce the alloy spike phenomena. The aluminum alloy film 55B isdeposited by the sputtering method, for example, to have a thickness ofabout 600 to 800 nm!.

The aforementioned shunting word lines 55 are formed to have a wiringwidth of about 0.7 μm!, for example.

Thus, the memory cell array 11E of the DRAM 1 of the present embodimentis constructed of a totally six-layered multi-wiring structure which iscomposed of a four-layered gate wiring structure and an overlyingtwo-layered wiring structure. The former four-layered gate wiringstructure is composed of the gate electrodes 27 (or the word lines 27)of the memory cell selecting MISFETs Qs, the lower electrode layer 35and the upper electrode layer 37 of the information storing capacityelements C of the stacked structure, and the complementary data lines50. The latter two-layered wiring structure is composed of the columnselect signal lines 52 and the shunting word lines 55.

The CMOSes composing the peripheral circuits of the aforementioned DRAM1 are constructed, as shown at the righthand side of FIG. 1. Then-channel MISFETs Qn of the CMOS are formed in the principal surfaceportion of the p⁻ -type well regions 22 in the region which is enclosedby the element separating insulating film 23 and the p-type channelstopper region 24. The n-channel MISFETs Qn are composed mainly of thep⁻ -type well regions 22, the gate insulating film 26, the gateelectrodes 27, and a pair of n-type semiconductor regions 29 and a pairof n⁺ -type semiconductor region 32 providing the source regions and thedrain regions, respectively.

The p-type channel stopper region 24 enclosing the n-channel MISFETs Qnare formed at a fabrication step other than the p-type channel stopperregions 25A enclosing the memory cell selecting MISFETs Qs of theaforementioned memory cell M. The p-type channel stopper region 24 isformed by introducing a p-type impurity with the use of a mask sharedwith the mask for forming the element separating insulating film 23 andby activating the p-type impurity by a heat treatment of forming theelement separating insulating film 23. Since the p-type channel stopperregion 24 is formed at the step shared with the element separatinginsulating film 23, the amount of diffusion of the p-type impurity intothe side of the active regions is slightly large. Since, however, then-channel MISFETs Qn are made to have a larger size than that of thememory cell selecting MISFETs Qs, the amount of diffusion of theaforementioned p-type impurity is relatively small. As a result, then-channel MISFETs Qn have small influences of the narrow channel effect.On the contrary, none of the p-type impurity forming the p-type channelstopper region 24 is introduced into other than the principal surfaceportion of the inactive regions of the p⁻ -type well regions 22 so thatthe impurity concentration of the principal surface of the activeregions of the p⁻ -type well regions 22 can be dropped. In short, then-channel MISFETs Qn can have their threshold voltages dropped to reducethe substrate effect and to enhance the driving ability. Especially incase the n-channel MISFETs Qn are used as the output step circuit, asufficient output signal level can be retained.

The aforementioned p⁻ -type well regions 22, gate insulating film 26,gate electrodes 27 and n-type semiconductor regions 29 are individuallyformed at the fabrication step shared with the aforementioned memorycell selecting MISFETs Qs to have substantially similar functions. Inshort, the n-channel MISFETs Qn are constructed to have the LDDstructure.

The highly doped n⁺ -type semiconductor region 32 is constructed toreduce the individual specific resistances of the source regions and thedrain regions. The n⁺ -type semiconductor region 32 is regulated by theside wall-spacers 31, which are formed in self-alignment on the sidewalls of the gate electrodes 26, so that it is formed in self-alignmentwith the gate electrodes 27. The side wall spacers 31 regulates thelength, as taken in the gate length, of the n-type semiconductor regions29 constructing the aforementioned LDD structure. Since the side wallspacers 31 are formed of a single layer in the regions formed with then-channel MISFETs Qn, they can shorten the gate length of the n-typesemiconductor regions 29. These n-type semiconductor regions 29 arelightly doped to have a high resistance but are made short so that then-channel MISFETs Qn can improve the transmission conductance.

Of the n-channel MISFETs Qn, the n-channel MISFET Qn to be used in theinput/output step circuit is interfaced at the single power sourcevoltage Vcc (5 V!) with the external devices so that it is driven at thepower source voltage Vcc. This n-channel MISFET Qn is constructed tohave a gate length of about 8 μm!, for example, to damp the intensity ofthe electric field in the vicinity of the drain regions. On the otherhand, the n-channel MISFET Qn to be used in the internal circuits suchas the direct peripheral circuits or the indirect peripheral circuit isdriven by the lower power source voltage (about 3.3 V!) so as to reducethe power consumption. This n-channel MISFET Qn is constructed to have agate length within a range of about 0.8 to 1.4 μm!, for example, so asto increase the degree of integration, and the intensity of the electricfield in the vicinity of the drain regions is damped by introducing thelower power source voltage Vcc. The individual n-channel MISFETs Qn ofthose input/output step circuits and the internal circuits areconstructed to have a substantially identical structure merely bychanging the gate lengths and the power sources to be used. In otherwords, each of the n-channel MISFETs Qn of the input/output stepcircuits and the internal circuits can be composed of the gateinsulating film 26, the gate electrodes 27, the n-type semiconductorregions 29 and the n⁺ -type semiconductor region 32. Moreover, theindividual n-channel MISFETs Qn can be constructed to have asubstantially equal size in the gate length direction of the side wallspacers 31.

Thus, in the DRAM 1 including the n-channel MISFETs Qn of the LDDstructure to be used as the input/output step circuits and the n-channelMISFETs Qn of the LDD structure to be used as the internal circuits: theused voltage of the n-channel MISFETs Qs of the input/output stepcircuits is higher than the used voltage of the n-channel MISFETs Qn ofthe internal circuits; the gate length of the n-channel MISFETs Qn ofthe input/output step circuits is made longer than that of the n-channelMISFETs Qn of the internal circuits; and the gate lengths of the lightlydoped n-type semiconductor regions 29 forming the LDD structure of then-channel MISFETs Qn of the input/output step circuits and the internalcircuits are made substantially equal. Thanks to this construction, then-channel MISFETs Qn are enabled to improve the hot carrier withstandvoltage by enlarging the gate length thereby to reduce the aging of thethreshold voltage and improve the electric characteristics. At the sametime, The n-channel MISFETs Qn of the internal circuits are enabled toretain the hot carrier withstand voltage by using the lower power sourcevoltage Vcc and to reduce the power consumption by using the lower powersource voltage Vcc. Moreover, the n-channel MISFETs Qn of theinput/output step circuit have their gate length enlarged, and then-channel MISFETs Qn of the internal circuits are enabled to improve thehot carrier withstand voltage by using the lower power source voltageVcc. As a result, the gate lengths of the lightly doped n-typesemiconductor regions 29 forming the aforementioned LDD structure can beindependently controlled so that the gate lengths of the lightly dopedn-type semiconductor regions 29 of the n-channel MISFETs Qn of theinternal circuits (or the gate lengths of the side wall spacers 31) canbe made substantially equal. In short, the DRAM 1 can reduce the powerconsumption and improve the hot carrier withstand voltage, and thenumber of steps for fabricating the n-channel MISFETs Qn can be reduced,as will be described hereinafter.

With the n⁺ -type semiconductor region 32 of the n-channel MISFETs Qnthus far described, there are connected wiring lines 52 throughconnecting holes 51C which are formed in the interlayer insulating film40 and the interlayer insulating film 51. The wiring lines 52 are formedof the lower wiring line of the two-layered wiring structure which ismade common with the aforementioned column select signal lines 52.

The p-channel MISFETs Qp of the CMOS are constructed in the principalsurface portions of the n⁻ type well regions 21 within regions enclosedby the element separating insulating film 23. The p-channel MISFETs Qpare composed mainly of the n⁻ -type well region 21, the gate insulatingfilm 26, the gate electrodes 27, and a pair of p-type semiconductorregions 30 and a pair of p⁺ -type semiconductor region 39 providing thesource regions and the drain regions.

The n⁻ -type well region 21, the gate insulating film 26 and the gateelectrodes 27 are constructed to have functions substantially similar tothose of the memory cell selecting MISFETs Qs and the n-channel MISFETsQn.

The lightly doped p-type semiconductor regions 30 are composed of thep-channel MISFETs Qp having the LDD structure. Densely doped p⁺ -typesemiconductor regions 39 are formed in self-alignment with the side wallspacers 31 and 33C which are formed on and in self-alignment with theside walls of the gate electrodes 27. In other words, the densely dopedp⁺ -type semiconductor regions 39 of the p-channel MISFETs Qp are formedto have a two-layered structure in which the side wall spacers 33C arelaminated on the side walls of the side wall spacers 31. These side wallspacers 31 and 33C are constructed to have a longer gate length to anextent corresponding to the side wall spacers 33C than that of the sidewall spacers 31 of the n-channel MISFETs Qn. More specifically, the sidewall spacers 31 and 33C are enabled to reduce the amount of diffusion ofthe p⁺ -type semiconductor regions 39 into the channel forming regionsof the p-type impurity by having their gate lengths enlarged, so thatthey can reduce the short channel effect of the p-channel MISFETs Qpwhile retaining the effective channel length. Since the p-type impurityhas a larger diffusion coefficient than that of the n-type impurity, thep-channel MISFETs Qp are constructed to have the aforementionedstructure.

In the DRAM 1 including the n-channel MISFETs Qn of the LDD structureand the p-channel MISFETs Qp of the LDD structure, the gate lengths ofthe side wall spacers 31 and 33C formed on and in self-alignment withthe side walls of the gate electrodes of the p-channel MISFETs Qp aremade longer than the gate lengths of the side wall spacers 31 which areon and in self-alignment with the gate electrodes 27 of the n-channelMISFETs Qn. Thanks to this construction, the gate lengths of the sidewall spacers 31 of the n-channel MISFETs Qn can be made shorter than thegate lengths of the lightly doped n-type semiconductor regions formingthe LDD structure. As a result, the transmission conductance of then-channel MISFETs Qn can be improved to increase the operating speed. Atthe same time, the gate lengths of the side wall spacers 31 and 33C ofthe p-channel MISFETs Qp can be elongated to reduce the go-round of thedensely doped p⁺ -type semiconductor regions 39 to the channel formingregions thereby to reduce the short channel effect of the p-channelMISFETs Qp so that a high degree of integration can be achieved.

With the p⁺ -type semiconductor regions 39 of the p-channel MISFETs Qp,there are connected with the wiring lines 52 through the aforementionedconnecting holes 51C.

As shown at the righthand side of FIG. 1, the wiring lines 52 areconnected with the upper wiring lines 55 through a transition-metal film54 which is buried in connecting holes 53D formed in the inter-layerinsulating film 53. The wiring lines 55 extending over the interlayerinsulating film 53 are formed of the upper wiring layer having atwo-layered wiring structure which is shared with the aforementionedshunting word lines 55. The transition-metal film 54 buried in theconnecting holes 53D is formed of a W film which is deposited by theselective CVD method selectively over the surfaces of the wiring lines52 exposed from the insides of the connecting holes 53D. Thetransition-metal film 54 is formed to improve the step coverage in thestepped shape which is formed by the connecting holes 53D of the wiringlines 55.

The wiring lines 55 (including the shunting word lines 55) are formed ofa composite film in which the transition-metal nitride film 55A and thealuminum alloy film 55B are sequentially laminated, as has beendescribed hereinbefore. The wiring lines 55 have their signaltransmission rate determined mainly by the upper aluminum alloy film55B. In case Si is added to the upper aluminum alloy film 55B, the lowertransition-metal nitride film (or the transition-metal silicide film)55A of the wiring lines 55 is formed all over those regions between theupper aluminum alloy film 55B and the interlayer insulating film 53,which include the connected portions of the wiring lines 55 and thetransition-metal film 54 buried in the connecting holes 53D. In short,the wiring lines 55 have their underlying material below the upperaluminum alloy film 55B homogenized at the portions of the connectingholes 53D and the interlayer insulating film 53. On the other hand, thelower transition-metal nitride film 55A of the wiring lines 55 has ahigher migration withstand voltage than that of the upper aluminum alloyfilm 55B. In short, even if the aluminum alloy film 55B is broken due tothe migration phenomena, the signals can be transmitted through thelower transition-metal nitride film 55A so that the defects such as thedisconnections of the wiring lines 55 can be reduced.

Thus, in the DRAM 1 for connecting the transition-metal film 54, whichare buried by the selective CVD method in the connecting holes 53Dformed in the underlying interlayer insulating film 53 and the aluminumalloy film 55B extending over the interlayer insulating film 53 andcontaining the Si added thereto, the transition-metal nitride film (orthe transition-metal silicide film) 55A is formed between the aluminumalloy film 55B and the underlying interlayer insulating film 53 andbetween the transition-metal film 54 buried in the connecting holesinterlayer insulating film 53 and the aluminum alloy film 55B. Thanks tothis construction, the underlying layer of the aluminum alloy film 55Bcan be homogenized over the transition-metal film 54 buried in theconnecting holes 53D and the interlayer insulating film 53 so that theSi added to the aluminum alloy film 55B can be less deposited at theinterface between the transition-metal film 54 buried in the connectingholes 53D and the aluminum alloy film 55B thereby to reduce theresistance of the aforementioned interface. Even if, moreover, thealuminum alloy film 55B is broken due to the migration phenomena, forexample, the transition-metal nitride film 55A formed below the aluminumalloy film 55B can connect the aluminum alloy film 55B through thosebroken portions to reduce the defects of the disconnections of thewiring lines 55.

In case the Cu is added to the upper aluminum alloy film 55B, the wiringlines 55 (including the shunting word lines 55) are formed with thetransition-metal nitride film 55A at the connected portions (includingtheir interface portions) at least between the aluminum alloy film 55Band the transition-metal film 54 buried in the connecting holes 53D. Thetransition-metal nitride film 55A have actions as a barrier, as has beendescribed hereinbefore. In short, the wiring lines 55 are formed toprevent the alloying reaction due to the mutual diffusions between thealuminum of the upper aluminum alloy film 55B and the W of thetransition-metal film 54 buried in the connecting holes 53D.

Thus, in the DRAM 1 for connecting the transition-metal film 54 buriedby the selective CVD method in the connecting holes 53D formed in theunderlying interlayer insulating film 53 and the aluminum alloy film 55Bextending over the interlayer insulating film 53 and containing the Cuadded thereto, the transition-metal nitride film 55A having the barrieraction is sandwiched between the transition-metal film 54 buried in theconnecting holes 53D and the aluminum alloy film 55B. Thanks to thisconstruction, in the interface between the transition-metal film 54buried in the connecting holes 53D and the aluminum alloy film 55B, thealloying reaction due to the mutual diffusions of the transition metaland the aluminum can be prevented to reduce the resistance of theaforementioned interface.

The lower transition-metal nitride film 55A of the wiring lines 55 to bepositively used has a crystal orientation of (200), as has beendescribed hereinbefore. FIG. 8 presents the relations between the targetvoltage KW! and the specific resistances μΩ-cm! when in the sputteringtreatment. Data (A) and (B) plot the distances of the TiN film, which isdeposited by the sputtering method on the surface of the semiconductorwafer, from the center of the semiconductor wafer. The data (A)indicates the characteristics of the TiN film for the 0 μm! from thecenter of the semiconductor wafer, i.e., at the center of thesemiconductor wafer. The data (B) indicates the characteristics of theTiN film for the 50 μm! from the center of the semiconductor wafer.

As seen from the data (B) in FIG. 8, the TiN film has the lower specificresistance for the longer distance from the center of the semiconductorwafer.

FIG. 9 (plotting the relation between the incidental angle of an X-rayand the X-ray diffraction intensity) presents the result of theexperiment that the TIN film was exposed to the X-ray diffractionspectrum in a region C having a high specific resistance such as about460 μΩ-cm!. On the other hand, FIG. 10 (plotting the relation betweenthe incidental angle of an X-ray and the X-ray diffraction intensity)presents the result of the experiment that the TiN film was exposed tothe X-ray diffraction spectrum in a region D having a low specificresistance such as about 400 μΩ-cm!. In the region having the highspecific resist ance, as shown in FIG. 9, the TiN film has mixed crystalorientations of (111) and (200). As shown in FIG. 10, on the contrary,the Ti N film h as a single crystal orientation of (200). In otherwords, the TiN film having the crystal orientation of (200) has a lowerspecific resistance than that of the TiN film having the mixed crystalorientations of (111) and (200), as shown in FIG. 8, that it hasphysical properties of the higher film density. As a result, the TiNfilm having the crystal orientation of (200) is featured by an excellentheat resistance (acting as the barrier) and can reduce the deposition ofthe Si.

Thus, the lower transition-metal nitride film 55A of the aforementioned(33-18) wiring lines 55, namely, at least the transition-metal nitridefilm 55A between the transition-metal film 54 buried in theaforementioned connecting holes 53D and the upper aluminum alloy film55B is made of the TiN film having the crystal orientation of (200).Thanks to this construction, the TIN film having the crystal orientationof (200) can have a lower deposition of the Si than that of the TiN filmhaving the crystal orientation of (111) or the TIN film having the mixedcrystal orientation of (111) and (200), so that it can reduce theresistance of the aforementioned interface (i.e., the interface between54 and 54B) the more. Because of the lower specific resistance than thatof the TiN film having the above-specified other crystal orientations,moreover, the resistance at the interface can be reduced the more.Because of the higher film density, still moreover, the barrier actioncan be improved the better.

As shown in FIG. 1 and FIG. 15 (presenting an essential section showingthe sectional structure at a position different from that of FIG. 1), inthe regions of the peripheral circuits of the DRAM 1, the lower wiringlines of the two-layered wiring structure are formed of theaforementioned transition-metal film, because their wiring width isshrunk by the high integration so that the migration withstand voltagecannot be retained by the aluminum film or its alloy film. Theperipheral circuits, especially the direct peripheral circuits arearranged with the n-channel MISFETs Qn and the p-channel MISFETs Qp in amanner to correspond to the array pitch of the memory cells M of thememory cell arrays 11E so that the wiring lines 52 have strict layoutrules.

In the regions of the peripheral circuits, on the other hand, the mutualdiffusions of the impurities are caused in case the n⁺ -typesemiconductor region 32 of the n-channel MISFETs Qn and the p⁺ -typesemiconductor regions 39 of the p-channel MISFETs Qp are connected or incase the wiring lines are formed of the transition-metal silicide filmor its laminated film (e.g., the same conducting layer as that of thecomplementary data lines 50). Therefore, the wiring lines 52 used aremade of not the same conducting layer as that of the complementary datalines 50 used in the aforementioned memory cell arrays 11E but theaforementioned transition-metal film freed from the aforementionedmutual diffusions of the impurities.

Thus, in the DRAM 1 including: the complementary data lines, theshunting word lines and the column select signal lines over the memorycell arrays 11E; and the two wiring layers in the regions of theperipheral circuits of the memory cell arrays 11E: the complementarydata lines 50 over the memory cell arrays 11E are formed of thecomposite film, in which the polycrystalline silicon film 50A and thetransition-metal silicide film 50B deposited by the CVD method aresequentially laminated; the aforementioned column select signal lines 52are formed of the transition-metal film which is deposited over thecomplementary data lines 50 by the sputtering method; the aforementionedshunting word lines 55 are formed of the aluminum alloy film 55B(including the transition-metal nitride film 55A) deposited by thesputtering method; the same conducting layer (55) as the shunting wordlines 55 and the same conducting layer (52) as the underlying columnselect signal lines 52 are connected through the transition-metal film54 which is buried by the selective CYD method in the connecting holes53D formed in the interlayer insulating film 53 inbetween; the upperwiring lines 52 of the two wiring layers in the regions of theaforementioned peripheral circuits are formed of the same conductinglayer as that of the aforementioned column select signal lines 52whereas the-upper wiring lines 55 are formed of the same conductinglayer as that of the aforementioned shunting word lines 55; and thelower wiring lines 52 and upper wiring lines 55 of the two wiring linelayers are connected through the transition-metal film 54 which isburied in the connecting holes 53D by the aforementioned selective CVDmethod. Thanks to this construction, the following effects can beachieved:

(1) The complementary data lines 50 over the aforementioned memory cellarrays 11E can reduce the defects such as the disconnections becausethey are excellent in the resistances to the heat treatment and theoxidation and because they have a high step coverage for thepolycrystalline silicon film 50A deposited by the CVD method the lowerlayer. Moreover, the complementary data lines 50 can improve the stepcoverage better to reduce the defects such as the disconnections becausetheir upper transition-metal silicide film 50B is deposited by the CVDmethod.

(2) The aforementioned column select signal lines 52 are formed over thecomplementary data lines 50 so that they can be extended substantiallystraight without bypassing the connected portions (i.e., the connectingholes 40A) between the complementary data lines 50 and the memory cellsM. As a result, the signal transmission rate can be raised to increasethe speeds of the information writing operations and the informationreading operations. At the same time, the column select signal lines 52are formed of a layer different from that of the complementary datalines 50 so that the wiring gap between the lower complementary datalines 50 can be shrunk to improve the degree of integration.

(3) The wiring lines 55 have a lower resistance than the lowercomplementary data lines 50 and the column select signal lines 52 sothat their resistance can be reduced to increase the speeds of theinformation writing operations and the information reading operations.

(4) The transition-metal film 54 for connecting the same conductivelayer 52 as the aforementioned column select signals 52 and the sameconducting layer (55) as the shunting word lines 55 can compensate thestep coverage at the connected portions of the same conducting layer(55) as the upper shunting word lines 55 to reduce the defects such asthe disconnections of the conducting layer (55). The transition-metalfilm 54 is enabled to reduce the stress with the underlyingtransition-metal film (52) by forming the underlying conducting layer(52) of the same transition-metal film (52).

(5) The lower wiring lines 52 of the regions of the aforementionedperipheral circuits, especially the direct peripheral circuits )e.g.,the sense amplifier circuits or the decoder circuits) of theaforementioned memory cell arrays 11E are formed of the transition-metalfilm so that their migration withstand voltage can be raised to shrinkthe width of the wiring lines 52 (by aligning them with the arrangementpitch of the memory cells M) thereby to improve the degree ofintegration.

As shown in FIG. 1, the shunting word lines 55 and the wiring lines 55of the DRAM 1 are overlaid by a passivation film 56. This passivationfilm 56 is formed of a composite film in which a silicon oxide film 56Aand a silicon nitride film 56B are sequentially laminated.

The lower silicon oxide film 56A is constructed to flatten its surface,i.e., the underlying surface of the upper silicon nitride film 56B. Thelower silicon oxide film 56A is deposited at such a temperature as toleave the aluminum alloy film 55B unmelted, because the aluminum alloyfilm 55B is formed over the underlying shunting word lines 55 and wiringlines 55. Specifically, the lower silicon oxide film 56A is deposited bythe C-CVD method using the tetraethoxysilane gases as its source gases,for example. Since the step coverage at the stepped portions of theunderlying surface is excellent, the lower silicon oxide film 56A isformed to have a thickness as large as or more than one half between theshunting word lines 55 or the wiring lines 55 in the regions, in whichthe aspect ratio of the gap between the shunting word lines 55 or thewiring lines 55 to their film thickness, so that it may have its surfaceflattened. The regions having the aforementioned aspect ratio of 1 ormore correspond to or near the minimum wiring gap, and the step coverageof the aforementioned upper passivation film 56 raises no problem in theregions having the aspect ratio of 1 or less. Since the shunting wordlines 55 are formed to have a wiring gap of about 0.7 μm!, theaforementioned 56a are formed to have a thickness of about 350 to 500nm!.

The upper silicon nitride film 56B of the aforementioned passivationfilm 56 is formed to improve the moisture resistance. The siliconnitride film 56B is deposited by the plasma CVD method, for example, tohave a thickness of about 1,000 to 1,200 nm!. This upper silicon nitridefilm 56B can prevent any formation of cavities due to the growth of theoverhang shape at the underlying stepped portions, because the lowersilicon oxide film 56A has its surface flattened.

Thus, in the DRAM 1 having the passivation film 56 formed over thewiring lines 55 formed mainly of the aluminum alloy film 55B, thepassivation film 56 is formed of the composite film, in which thesilicon oxide film 56A deposited by the C-CVD method using thetetraethoxysilane gases as its source gases and the silicon nitride film56B deposited by the plasma CVD method are sequentially laminated, andthe lower silicon oxide film 56A of the passivation film 56 is formed tohave a thickness equal to or more than one half of the gap of the wiringlines 55 of the regions, in which the aspect ratio of the gap of thewiring lines 55 and the thickness of the wiring lines 55 is 1 or more.Thanks to this construction, the lower silicon oxide film 56A of thepassivation film 56 can be deposited at such a low temperature as toleave the aluminum alloy film 55B of the wiring lines 55 unmelted and ata high step coverage, so that the step shape formed of the wiring lines55 can be flattened. The upper silicon nitride film 56B of an excellentmoisture resistance of the aforementioned passivation film 56 can beformed without forming any cavity due to the aforementioned steppedshape. As a result, no cavity is formed in the upper silicon nitridefilm 56B of the passivation film 56 is formed so that neither thecracking of the passivation film 56 nor the water reservation in thecavity can be caused to improve the moisture resistance of thepassivation film 56.

The boundary regions of the memory cell arrays (MA) 11E and theperipheral circuits of the aforementioned DRAM 1 are constructed, asshown in FIG. 11 (presenting a schematic top plan view) and FIG. 12(presenting an enlarged top plan view of the essential portion of FIG.11). Specifically, the p-type channel stopper regions 25A, which areformed in the inactive regions of the memory cell array lE, and thep-type channel stopper regions 24, which are formed in the inactiveregions of the peripheral circuits, are not overlapped at theaforementioned boundary regions. Since the p-type channel stopperregions 25A of the memory cell arrays 11E and the p-type channel stopperregions 24 of the peripheral circuits are formed at differentfabrication steps, they are not overlapped at the boundary regions todrop the impurity concentration of the inactive regions or the boundaryregions. As a result, it is possible to raise the pn junction withstandvoltage between each of the n-type semiconductor regions 29 and n⁺ -typesemiconductor region 32 formed in the active regions and the principalsurface portions of the boundary regions of the p⁻ -type well regions22. Since, however, the principal surface of the inactive regions of theboundary regions of the p⁻ -type well regions 22 has a low impurityconcentration, the threshold voltage of the parasitic MOS is liable tobe dropped to form the n-type inverted layer. This n-type inverted layeris formed to have a large area to enclose the memory cell array 11E. Ifan active region is present across or near the aforementioned boundaryregions, its area is increased to an extent corresponding to the area ofthe aforementioned n-type inverted layer. This apparently augments thepn-junction area to increase the amount of the leakage current at the pnjunction. As shown in FIG. 12, therefore, the n-channel MISFET Qn of anactive region Act, e.g., the peripheral circuit is isolated from theboundary region (nor across the boundary region). This isolation issized by considering at least the masking displacement at thefabrication step and the amount of diffusions of the n-type impurity ofthe n-type semiconductor regions 29 and the n⁺ -type semiconductorregion 32.

On the other hand, the boundary regions between the aforementionedmemory cell array (MA) 11E and the peripheral circuit may beconstructed, as shown in FIG. 13 (presenting a schematic top plan view)and FIG. 14 (presenting an enlarged top plan view showing the essentialportion of FIG. 13). Specifically, the p-type channel stopper regions25A of the memory cell array 11E and the p-type channel stopper regions24 of the peripheral circuit are superposed at the aforementionedboundary region. This superposition corresponds to at least the maskingallowance at the fabrication step. In case the p-type channel stopperregions 24 and 25A are superposed, the impurity concentration of theboundary region of the inactive regions is increased. If the impurityconcentration of the principal surface portion of the inactive region ofthe p⁻ -type well regions 22 is raised, the threshold voltage of theparasitic MOS can be raised to improve the isolating ability but todeteriorate the pn junction withstand voltage between the n-typesemiconductor regions 29 and the n⁺ -type semiconductor region 32 formedin the boundary region and the active region. As shown in FIG. 14,therefore, the n-channel MISFET Qn of the active region Act, e.g., theperipheral circuit is isolated from the boundary region. This isolationis sized by considering at least the masking displacement at thefabrication step and the amounts of diffusions of the n-type impuritiesof the p-type channel stopper regions 24 and 25A and the n-typeimpurities of the n-type semiconductor regions 29 and the n⁺ -typesemiconductor region 32.

The aforementioned boundary region is usually arranged with a not-shownguard ring region for preventing the minority carriers generated by thesubstrate potential generator circuit (i.e., the V_(BB) generatorcircuit) 1703 from migrating into the memory cell array 11E. This guardring region is arranged around the memory cell array 11E and is composedof the n-type semiconductor regions 29 or the n⁺ -type semiconductorregion 32. The guard ring region is formed in the memory cell array 11E(isolated from the boundary region) or inside of the boundary region ofeach of the aforementioned p-type channel stopper regions 25A and 24.Above the guard ring region, there are formed either the lower electrodelayers 35 and the upper electrode layers 37 of the information storingcapacity elements C of the stacked structure of the aforementionedmemory cells or a step damping layer formed of the same conducting layeras the former layers. This step damping layer damps the stepped shape,which is formed between the memory cell array 11E and the peripheralcircuit, to improve the treating accuracy of the upper wiring lines suchas the column select signal lines 52 and the shunting word lines 55 andto reduce the defects such as the disconnections.

Thus, in the DRAM 1 arranged with the n-channel MISFETs Qn of the memorycells M and the peripheral circuits in the different active regions ofthe p⁻ type well regions 22, which are enclosed by the p-type channelstopper regions formed in the principal surface portions of the inactiveregions of the p⁻ -type well regions 22, the p-type channel stopperregions 25A enclosing the memory cells M and the p-type channel stopperregions 24 enclosing the n-channel MISFETs Qn of the peripheral circuitsare independently formed at the different fabrication steps, and theindividual boundary regions of the p-type channel stopper regions 24 arenot arranged with the active regions Act such as the n-channel MISFETsQn of the memory cells M and the peripheral circuits. Thanks to thisconstruction, in case the p-type channel stopper regions 25A and thep-type channel stopper regions 24 are isolated by the aforementionedboundary region, this boundary region is liable to be formed with alarge n-type inverted layer corresponding to the area thereof. If theactive region Act is present in the boundary region, the areas of then-type semiconductor regions 29 and the n⁺ -type semiconductor region 32to be formed in the active region is apparently increased to an addedextent of the aforementioned n-type inverted layer so that the amount ofthe leakage current is augmented at the junction between the p⁻ -typewell regions 22 and the n-type semiconductor regions 29 or the n⁺ -typesemiconductor region 32. Since, however, the active region Act is notarranged in the aforementioned boundary region, the amount of theleakage current can be reduced at the aforementioned junction. In case,on the other hand, the p-type channel stopper regions 25A and the p-typechannel stopper regions 24 are superposed at the boundary region, thisregion has its impurity concentration increased. Since, however, theboundary region is not arranged with the active region Act, it ispossible to improve the pn junction withstand voltage between the p⁻-type well regions 22 and the n-type semiconductor regions 29 or the n⁺-type semiconductor region 32.

Next, the specific process for fabricating the aforementioned DRAM 1will be briefly described with reference to FIGS. 16 to 49 (presentingsectional views showing the essential portions at the individualfabrication steps).

Fist of all, the p⁻ -type semiconductor substrate 20 made of singlecrystalline silicon is prepared.

Well Forming Step!

Next, there are sequentially laminated over the principal surface of theaforementioned p⁻ -type semiconductor substrate 20 a silicon oxide film60 and a silicon nitride film 61. The silicon oxide film 60 is formed bythe steam oxidization method at a temperature as high as about 900 to1,000 ° C.! to have a thickness of about 40 to 50 nm!. This siliconoxide film 60 is used as a buffer layer. The latter silicon nitride film61 is used as an impurity introducing mask and an non-oxidizable mask.This silicon nitride film 61 is deposited by the CYD method, forexample, to have a thickness of about 40 to 60 nm!.

Next, the silicon nitride film 61 is removed from the n⁻ -type wellregion (21) to form the mask. This formation of the mask (61) isaccomplished by using the photolithography technology (i.e., thetechnology for forming a photoresist mask) and the etching technology.

Next, as shown in FIG. 16, the aforementioned mask (61) is used to dopethe principal surface portion of the p⁻ -type semiconductor substrate 20with an an-type impurity 21n through the silicon oxide film 60. Then-type impurity 21n used is P having an impurity concentration of 10¹³atoms/cm₂ !, for example, and is introduced by the ion implantationhaving an energy of about 120 to 130 KeV!.

Next, the aforementioned mask 16 is used, as shown in FIG. 17, to growthe silicon oxide film 60 exposed from the mask, thereby to form athicker silicon oxide film 60A. This silicon oxide film 60A is formedonly in the n⁻ -type well region (21) and is used as the mask forremoving the aforementioned mask (61) and the impurity introducing mask.The silicon oxide film 60A is formed by the steam oxidation method at atemperature as high as about 900 to 1,000 ° C.! until it has a thicknessof about 110 to 130 nm!, for example. The heat treatment step forforming this silicon oxide film 60A diffuses the introduced n-typeimpurity 21n slightly.

Next, the aforementioned mask (61) is selectively removed with hotphosphoric acid, for example.

Next, as shown in FIG. 18, the aforementioned silicon oxide film 60A isused as the impurity introduction mask to dope the principal surfaceportion of the p⁻ -type semiconductor substrate 20 with a p-typeimpurity 22p through the silicon oxide film 60. This p-type impurity 22pused is B (or BF₂) at an impurity concentration of about 10¹² to 10¹³atom/cm² ! and is implanted by the ion implantation with the energy ofabout 20 to 30 KeV!. This p-type impurity 22p is not introduced into theregion to be formed with the n⁻ -type well region (21), because thesilicon oxide film 60A is made thick.

Next, the aforementioned n-type impurity 21n and p-type impurity 22p areindividually extended and diffused to form the n⁻ -type well regions 21and the p⁻ -type well regions 22, as shown in FIG. 19. These n⁻ -typewell regions 21 and p⁻ -type well regions 22 are formed by the heattreatment in the atmosphere at a temperature as high as about 1,100 to1,300 ° C.!. As a result, the p⁻ -type well regions 22 is formed inself-alignment with the n⁻ -type well regions 21.

Separate Region Forming Step!

Next, the aforementioned silicon oxide films 60 and 60A are removed toexpose the individual principal surfaces of the n⁻ -type well regions 21and the p⁻ -type well regions 22 to the outside.

Next, as shown in FIG. 20, a silicon oxide film 62, a silicon nitridefilm 63 and a polycrystalline silicon film 64 are sequentially laminatedover the individual principal surfaces of the n⁻ -type well regions 21and the p⁻ -type well regions 22. The lower silicon oxide film 62 isformed by the steam oxidization method at a high temperature of about900 to 1,000 ° C.!, for example, to have a thickness of about 15 to 25nm!. The intermediate silicon nitride film 63 is used mainly as anon-oxidizable mask. This silicon nitride film 63 is deposited by theCVD method, for example, to have a thickness of 150 to 250 nm!. Theupper polycrystalline silicon film 64 is used mainly as an etching maskof the lower silicon nitride film 63, a groove depth judging mask and aside wall spacer length controlling mask. The polycrystalline siliconfilm 64 is deposited by the CVD method, for example, to have a thicknessof about 80 to 120 nm!.

Next, as shown in FIG. 21, the upper polycrystalline silicon film 64 isremoved from the principal surfaces of the individual inactive regionsof the n⁻ -type well region n⁻ -type well regions 21 and the p⁻ -typewell regions 22 to form the mask of the polycrystalline silicon film 64remaining on the active regions. This mask (64) is formed by thephotolithography technology and the etching technology. After the mask(64) has been formed, there is removed the etching mask (i.e., thephotoresist film) which is formed by the aforementioned photolithographytechnology.

Next, as shown in FIG. 22, the aforementioned mask (64) is used toremove the silicon nitride film 63, which is exposed to the inactiveregions, thereby to form the mask (63) below the mask (64). Thepatterning of the mask (63) is accomplished by using not the photoresistfilm for patterning the mask (64) but the mask (64) so that thecontaminants from the photoresist film may be prevented from beingtrapped by the individual principal surfaces of the n⁻ -type wellregions 21 and the p⁻ -type well regions 22 and by the silicon oxidefilm 62.

Next, as shown in FIG. 23, a silicon nitride film 65 and a silicon oxidefilm 66 are sequentially laminated all over the surfaces including thatof the aforementioned mask (64). The lower silicon nitride film 65 isused mainly as a non-oxidizable mask and is made thinner than theaforementioned mask (63). This silicon nitride film 65 is deposited bythe CVD method, for example, to have a thickness of about 15 to 25 nm!.The upper silicon oxide film is used mainly as an etching mask. Thissilicon oxide film 66 is deposited by the CVD method using inorganicsilane gases (SiH₄ or SiH₂ Cl₂) and nitrogen oxide gases (N₂ O), forexample, as its source gases to have a thickness of about 150 to 250nm!.

Next, as shown in FIG. 24, the aforementioned silicon oxide film 66 andsilicon nitride film 65 are anisotropically etched to an extentcorresponding to the individual deposited thicknesses to form the masks(65) and (66) on and in self-alignment with the individual side walls ofthe aforementioned masks (63) and (64). The masks (65) and (66) areformed as the so-called "side wall spacers".

Next, as shown in FIG. 25, the aforementioned masks (64) and (66) areused as the etching masks to form shallow grooves 67 in the individualinactive regions of the n⁻ -type well regions 21 and the p⁻ -type wellregions 22. These shallow grooves 67 are so formed to enhance theelement separating ability that the depths below the element separatinginsulating film (23) to be formed at a later step than the junctiondepth of the n-type semiconductor regions (29) and (32), for example.The depth of the shallow grooves 67 is controlled by the thickness ofthe aforementioned mask (64). Specifically, the shallow grooves 67 areformed, and the mask (64) is removed. The reactive gas components ofthis mask (64) are detected so that the etching step for forming theshallow grooves 67 is stopped at or neat the instant when the reactivegas components of the mask (64) are exhausted. The shallow grooves 67are formed by the anisotropic etching such as the RIE method to have adepth of about 80 to 120 nm!.

Thus, the mask (64) made of a material having an etching ratesubstantially equal to those of the n⁻ -type well regions 21 and the p⁻-type well regions 22 is used to form the shallow grooves by etching theprincipal surfaces of the individual inactive regions of the n⁻ -typewell regions 21 and the p⁻ -type well regions 22 to an extentcorresponding to the thickness of the aforementioned mask (64). Thanksto this construction, the depth of the shallow grooves 67 can becontrolled by the thickness of the mask (64) so that its controllabilitycan be improved.

Next, a silicon oxide film 62A is formed over the principal surfaces ofthe individual inactive regions of the n⁻ -type well regions 21 and thep⁻ -type well regions 22, which are exposed as a result of forming theshallow grooves 67. This silicon oxide film 62A is used as a bufferlayer when an impurity is introduced. The silicon oxide film 62A isformed by the thermal oxidization method to have a thickness of about 8to 12 nm!.

Next, in the regions to be formed with the peripheral circuits as shownin FIG. 26, the principal surface portions of the inactive regions ofthe p⁻ -type well regions 22 are doped with a p-type impurity 24pthrough the aforementioned silicon oxide film 62A. For introducing thisp-type impurity 24p, the aforementioned masks (63) and (66) and anot-shown photoresist mask are used as the impurity introduction mask.The p-type impurity 24p used is BF₂ having an impurity concentration ofabout 10¹³ atoms/cm² !, for example, and is introduced by the ionimplantation using an energy of about 50 to 70 KeV!. This p-typeimpurity 24p is introduced in self-alignment with the active regionsinto the regions to be formed with the peripheral circuits.

Next, the aforementioned masks (63) and (65) are used mainly as thenon-oxidizable masks to form the element separating insulating film (orthe field insulating film) 23 at the portions of the silicon oxide film62A of the individual inactive regions of the n⁻ -type well regions 21and the p⁻ -type well regions 22. At this time, the silicon oxide film66 is removed with an etching liquid of a hydrofluoric acid before theelement separating insulating film 23 is formed. This element separatinginsulating film 23 can be formed by a heat treatment for about 30 to 40(minutes) in the nitrogen gas atmosphere containing a trace amount (nomore than about 1 %!) of oxygen at a considerably high temperature ofabout 1,050 to 1,150 ° C. !, for example, and by a subsequent steamoxidization method for about 30 to 50 minutes!. The element separatinginsulating film 23 is formed to have a thickness of about 400 to 600nm!, for example.

Since the end portions at the side of the active regions of the elementseparating insulating film 23 hold the thin mask (659 in direct contactwith the substrate, the growth in the transverse direction (toward theactive regions) at the initial stage of the oxidization is reduced.Since, moreover, the thick mask (63) can reduce the transverse growtheven if the oxidization proceeds, the bird's beak can be reduced. As theoxidization proceeds, on the other hand, the thin mask (65) can rise inthe form of the bird's beak to damp the stress thereby to reduce thedefects. In short, the element separating insulating film 23 has such asmall bird's beak to that it can be made thick. As a result, the elementseparating insulating film 23 can be sized substantially equally to themask (63) for forming it, so that it can shrink the separating areabetween the elements and increase the effective area of the activeregions.

As a result of the heat treatment for forming the element separatinginsulating film 23, the p-type impurity 24p introduced into theprincipal surface portions of the aforementioned p⁻ -type well regions22 is extended and diffused at the substantially identical fabricationstep to form the p-channel stopper regions 24. The p-type impurity 24pis diffused in the transverse direction (toward the active regions),too, but its amount of transverse diffusion itself is relatively smallbecause the n-channel MISFETs Qn of the peripheral circuits are madelarger than the memory cell selecting MISFETs Qs of the peripheralcircuits. In short, the n-channel MISFETs Qn have light influences ofthe narrow channel effect.

Next, the aforementioned masks (63) and (65) and the silicon oxide film62 are removed to expose the principal surfaces of the individual activeregions of the n⁻ -type well regions 21 and the p⁻ -type well regions22. After this, as shown in FIG. 27, a silicon oxide film 68 is formedover the individual principal surfaces of the n⁻ -type well regions 21and p⁻ -type well regions 22 thus exposed to the outside. This siliconoxide film 68 is used mainly to oxidize the so-called "white ribbon" ofsilicon nitrides which are formed at the end portions of the elementseparating insulating film 23 by the silicon nitride films (i.e., masks)63 and 65 used for forming the element separating insulating film 23.The silicon oxide film 68 is formed by the steam oxidization method at ahigh temperature of about 900 to 1,000 ° C.!, for example, to have athickness of about 40 to 100 nm!.

Next, in the regions to be formed with the memory cell array 11E, asshown in FIG. 28, the p⁻ -type well regions 22 has its principal surfaceportions formed thereover with the p-channel stopper regions 25A and thep-type semiconductor regions 25B. The p-type channel stopper regions 25Aare formed in the inactive regions below the element separatinginsulating film 23. The p-type semiconductor regions 25B are formed inthe active regions for forming the memory cells M. The p-type channelstopper regions 25A and the p-type semiconductor regions 25B areindividually formed, for example, by introducing B of an impurityconcentration of about 10¹² to 10¹³ atoms/cm² ! by the ion implantationmethod using a high energy of about 200 to 300 KeV!. The p-type impurityis introduced through the element separating insulating film 23 into theprincipal surface portions of the inactive regions of the p⁻ -type wellregions 22. In the principal surface portions of the active regions, thep-type impurity is introduced so deep into the principal surfaceportions of the p⁻ -type well regions 22 as to correspond to thethickness of the element separating insulating film 23. The p-typechannel stopper regions 25A and p-type semiconductor regions 25B thusformed are individually self-aligned with the element separatinginsulating film 23.

Thus, in the DRAM 1 formed with the memory cell selecting MISFETs Qsover the principal surface in the active regions enclosed by theinactive regions of the p⁻ -type well regions 22, the fabricationprocess comprises; the step of forming the first mask, in which themasks (63) and (64) are sequentially laminated over the principalsurface of the active regions of the p⁻ -type well regions 22; the stepof forming the second mask, in which the masks (65) and (66) madethinner than the mask (63) of said first mask and formed on and inself-alignment with the side walls of said first mask are sequentiallylaminated; the step of forming the shallow grooves 67 in the inactiveregions of the p⁻ -type well regions 22 by etching the principal surfaceof the inactive regions of the p⁻ -type well regions 22 by the use ofsaid first mask and said second mask; the step of forming the elementseparating insulating film (or the field insulating film) 23 over theprincipal surface of the inactive regions of the p⁻ -type well regions22 by the hot oxidizing treatment using said first mask and said secondmask; and the step of forming the p-type channel stopper regions 25Aover the principal surface portions of the p⁻ -type well regions 22below the element separating insulating film 23 by introducing thep-type impurity into all the principal surface portions including theactive regions and inactive regions of the p⁻ -type well regions 22after said first mask and said second mask have been removed. Thanks tothis construction, the amount of oxygen in the transverse direction ofthe element separating insulating film 23 can be reduced to reduce thesize of the element separating insulating film 23 while thickening thesame. By making use of the shallow grooves 67, the lower surface of theelement separating insulating film 23 can be made deeper than theprincipal surface of the active regions of the p⁻ -type well regions 22so that the separating size between the memory cell selecting MISFETs Qscan be increased in the depthwise direction of the p⁻ -type well regions22. As a result, the separating ability between the memory cellselecting MISFET Qs can be enhanced to thicken the element separatinginsulating film 23 so that the p-type impurity to be introduced into theprincipal surface portions of the active regions of the p⁻ -type wellregions 22 when it is introduced to form the p-type channel stopperregions 25A can be introduced deep into the p⁻ -type well regions 22. Asa result, it is possible to reduce the fluctuations of the thresholdvoltage of the memory cell selecting MISFETs Qs on the basis of theintroduction of the p-type impurity.

On the other hand, the step of forming the element separating insulatingfilm 23 is accomplished at the hot oxidization method at a temperaturewithin a range of about 1,050 to 1,150 ° C.!. Thanks to thisconstruction, the fluidicity of the silicon oxide film based upon thehot oxidization method is promoted when the element separatinginsulating film 23 is to be formed, so that the stress to be causedbetween the element separating insulating film 23 and the principalsurfaces of the individual inactive regions of the n⁻ -type well regions21 and the p⁻ -type well regions 22 can be reduced. As a result, it ispossible to reduce the crystal defects at the corners of the shallowgrooves 67 which are formed in the principal surface of the individualactive regions of the n⁻ -type well regions 21 and the p⁻ -type wellregions 22.

On the other hand, the shallow grooves 67 to be formed in the principalsurfaces of the individual inactive regions of the n⁻ -type well regions21 and the p⁻ -type well regions 22 may not be formed in case thecrystal defects cannot be restored or in case they are not especiallynecessary. In this case, the mask (64) may be eliminated, and the mask(65) may be made to have a thickness of 200 to 300 nm!.

Moreover, in the DRAM 1 in which the memory cell selecting MISFETs Qsforming the memory cells M and the n-channel MISFETs Qn forming theperipheral circuits are individually formed over the principal surfaceof the active regions of the p⁻ -type well regions 22 in the regionsenclosed by the inactive regions of the formed of the element separatinginsulating film 23 and the p-channel stopper regions, the principalsurface portions of the-active regions of the p⁻ -type well regions 22forming the memory cell selecting MISFETs Qs and the inactive regionsenclosing the former regions are formed at said inactive regions withthe p-channel stopper regions 25A by introducing the ptype impuritythrough the element separating insulating film and, at the inactiveregions enclosing the active regions for forming the n-channel MISFETsQn of the p⁻ -type well regions 22, with the p-type channel stopperregions 24 by introducing the p-type impurity 24p thereinto. Thanks tothis construction, the threshold voltage of the parasitic MOS is raisedat the aforementioned p-type channel stopper regions 25A to retain theseparating ability between the memory cells M and the memory cellselecting MISFETs Qs for forming the former and the memory cells Mtherearound. Moreover, the p-channel stopper regions 25A are formed inself-alignment with the aforementioned element separating insulatingfilm so that the p-type impurity for forming the p-channel stopperregions 25A can be little diffused to the active regions. As a result,it is possible to reduce the narrow channel effect of the memory cellselecting MISFETs Qs. At the same time, the p-type impurity 24p forforming the aforementioned p-type channel stopper regions 24 isintroduced only into the inactive regions but not into the activeregions for forming the aforementioned n-channel MISFETs Qn. As aresult, the influences of the substrate effect can be reduced to reducethe fluctuations of the threshold voltage of the n-channel MISFETs Qn.Since the n-channel MISFETs Qn are sized more than the memory cellselecting MISFETs Qs of the memory cells M, the n-channel MISFETs Qnhave a relatively small amount of diffusion of the p-type impurity 24pfor forming the p-channel stopper regions 24p to the active regions sothat they hardly establish the narrow channel effect. In the n-channelMISFETs Qn, moreover, the p-type impurity 24p for forming the p-typechannel stopper regions 24 is not introduced into the active regions sothat the impurity concentration in the surface of the active regions canbe reduced. As a result, the threshold voltage can be dropped to augmentthe drivability. The n-channel MISFETs Qn can retain the output signallevel sufficiently especially in case they are used in the output stepcircuit.

On the other hand, the memory cell selecting MISFETs Qs of the memorycells M and the n-channel MISFETs Qn are individually formed in theprincipal surface portions of the p⁻ -type well regions 22 having ahigher impurity concentration than that of the p⁻ -type semiconductorsubstrate 20. Thanks to this construction, the individual channelforming regions of the memory cell selecting MISFETs Qs and then-channel MISFETs Qn of the p⁻ -type well regions 22 can have theirimpurity concentrations increased to reduce the short channel effect. Atthe same time, potential barrier regions can be formed by the differencebetween the individual impurity concentrations of the p-type wellregions 22 and the p⁻ -type semiconductor substrate 20 so thatespecially the memory cells M can have their α-ray soft error withstandvoltage improved. Moreover, the n-channel MISFETs Qn can also have theirα-ray soft error withstand voltage improved in case they construct thedirect peripheral circuits such as the column address decoder circuits(YDEC) 12 or the sense amplifier circuits (SA) 13.

Gate insulating Film Forming Step!

Next, a silicon oxide film 68A is formed over the principal surface ofthe individual active regions of the n⁻ -type well regions 21 and the p⁻-type well regions 22. The silicon oxide film 68A is newly formed afterthe aforementioned silicon oxide film 68 has been removed. This newsilicon oxide film 68A may have a thickness of about 15 to 25 nm!.

Next in the regions to be formed with the peripheral circuits, as shownin FIG. 29, the principal surface portions of the active regions of then⁻ -type well regions 21 and the p⁻ -type well regions 22, which aredefined by the element separating insulating film 23, are doped with ap-type impurity 69p for adjusting the threshold voltage. This p-typeimpurity 69p used is B having an impurity concentration of about 10¹²atoms/cm² !, for example, and is introduced by the ion implantationmethod using an energy of about 20 to 30 KeV!. This p-type impurity 69pis introduced mainly to adjust the individual threshold voltages of then-channel MISFETs Qn and Qp. On the other hand, the p-type impurity 69pmay be introduced at different steps into the individual primary surfaceportions of the n⁻ -type well regions 21 and the p⁻ -type well regions22.

Next, the silicon oxide film 68A is selectively removed to expose theindividual principal surfaces of the p⁻ -type well regions 22 and the n⁻-type well regions 21.

Next, the gate insulating film 26 is formed over the individualprincipal surface of the p⁻ -type well regions 22 and n⁻ -type wellregions 21 thus exposed to the outside. The gate insulating film 26 isformed by the steam oxidization method at a temperature as high as about800 to 1,000 ° C.! to have a thickness of about 12 to 18 nm!.

Gate Wiring Line Forming Step!

Next, the whole surface of the substrate including the surfaces of thegate insulating film 26 and the element separating insulating film 23 isformed with a polycrystalline silicon film. This polycrystalline siliconsilicon film is deposited by the CVD method to have a thickness of about200 to 300 nm!. The polycrystalline silicon film is doped by the hotdiffusion method with an n-type impurity such as P for reducing theresistance. After this, the polycrystalline silicon film is formedthereover with a not-shown silicon oxide film by the hot oxidizationmethod. The polycrystalline silicon film is formed at the gate wiringline forming step of the first layer of the fabrication process.

Next, the polycrystalline silicon film is formed all over its surfacewith the interlayer insulating film 28. This insulating film 28 isformed by the CVD method using inorganic silane gases and nitrogen oxidegases as its source gases. The interlayer insulating film 28 is formedto have a thickness of about 250 to 350 nm!, for example.

Next, as shown in FIG. 30, a not-shown etching mask is sued to etch theinterlayer insulating film 28 and the polycrystalline silicon filmsequentially to form the gate electrodes 27 and the word lines (WL) 27.Moreover, the interlayer insulating film 28 is left over the gateelectrodes 27 and the word lines 27. The aforementioned etching isanisotropically accomplished.

Lightly Doped Semiconductor Region Forming Step!

Next, in order to reduce the contaminations due to the introduction ofthe impurity, the substrate is formed all over its surface with ansilicon oxide film (although not numbered). This silicon oxide film isformed over the individual principal surfaces of the p⁻ -type wellregions 22 and n⁻ -type well regions 21 exposed by the aforementionedetching and on the individual side walls of the gate electrodes 27 andthe word lines 27. The silicon oxide film is formed in the oxygenatmosphere at a temperature as high as about 850 to 950 ° C.!, forexample, to have a thickness of about 10 to 20 nm!.

Next, the element separating insulating film 23 and the interlayerinsulating film 28 (and the gate electrodes 27) are used as impurityintroduction masks to introduce an n-type impurity 29n into theprincipal surface portions of the p⁻ -type well regions 22 at theindividual regions for forming the memory cell arrays 11E and then-channel MISFETs Qn. The n-type impurity 29n is introduced inself-alignment with the gate electrodes 27. The n-type impurity 29n isintroduced by the ion implantation method of an energy of about 30 to 50KeV! by using P (or As) having an impurity concentration of about 10¹³atom/cm² !. When this n-type impurity 29n is to be introduced, althoughnot shown, the regions for forming the p-channel MISFETs Qp are coveredwith an impurity introduction mask (e.g., a photoresist film).

Next, as shown in FIG. 31, the element separating insulating film 23 andthe inter-layer insulating film (and the gate electrodes 27) are used asthe impurity introduction mask to dope the principal surface portions ofthe n⁻ -type well regions 21 with a p-type impurity 30p in the regionsfor forming the p-channel MISFETs Qp. This p-type impurity 30p isintroduced in self-alignment with the gate electrodes 27. The ptypeimpurity 30p used is B (or BF₂) having an impurity concentration ofabout 10¹² atoms/cm² !, for example, and is introduced by the ionimplantation method having an energy of about 20 to 30 KeV!. When thep-type impurity 30p is introduced, although not shown, the individualregions for forming the memory cell arrays 11E and the n-channel MISFETsQn are covered with an impurity introduction mask (or a photoresistfilm).

Densely Doped Semiconductor Region Forming Step 1!

Next, the side wall spacers 31 are formed on the individual side wallsof the aforementioned gate electrodes 27 and word lines 27 and theoverlying interlayer insulating film 28. These side wall spacers 31 canbe formed by depositing a silicon oxide film and by etching the siliconoxide film anisotropically by the RIE or the like to an extentcorresponding to the deposited thickness. The silicon oxide film of theside wall spacers 31 is formed by the CYD method using inorganic silanegases and nitrogen oxide gases as its source gases to have a thicknessequal to that of the aforementioned interlayer insulating film 28. Thissilicon oxide film is made to have a thickness of about 130 to 180 nm!,for example. The side wall spacers 31 acquire a gate length (taken inthe direction of the channel length) of about 150 nm!.

Next, as shown in FIG. 32, an n-type impurity 32n is introduced into theregions for forming the n-channel MISFETs Qn of the peripheral circuits.When the n-type impurity 32n is to be introduced, the side wall spacers31 are mainly used as an impurity introduction mask. On the other hand,the regions other than those for forming the n-channel MISFETs Qn, i.e.,the regions for forming the memory cell arrays 11E and the p-channelMISFETs Qp are covered, when they are to be doped with the n-typeimpurity 32n, with an impurity introduction mask (or a photoresistfilm). The n-type impurity 32n used is As (or P) having an impurityconcentration of about 10¹⁸ atoms/cm² !, for example, and is introducedby the ion implantation method of an energy of about 70 to 90 KeV!.

Next, as shown in FIG. 33, the aforementioned n-type impurity 29n,n-type impurity 32n and p-type impurity 30p are individually extendedand diffused by a heat treatment to form the n-type semiconductorregions 29, the n⁺ -type semiconductor regions 32 and the p-typesemiconductor regions 30 individually. The aforementioned heat treatmentis accomplished at a temperature as high as about 900 to 1,000 ° C.!,for example, for 20 to 40 minutes!. By forming the n-type semiconductorregions 29, the memory cell selecting MISFETs Qs having the LDDstructure of the memory cells M are completed. By forming the n-typesemiconductor regions 29 and the n⁺ -type semiconductor regions 32,moreover, the n-channel MISFETs Qn having the LDD structure arecompleted. These n-channel MISFETs Qn are used in the peripheralcircuits (for low voltages) and the input/output step circuits (for highvoltages) of the DRAM 1. On-the other hand, the p-type semiconductorregions 30 having the LDD structure of the p-channel MISFETs Qp arecompleted, but the p⁺ -type semiconductor regions 39 are formed afterthe completion of the memory cells M. Therefore, the p-channel MISFETsQp are formed at a later step.

Thus, in the DRAM 1 comprising the n-channel MISFETs Qn having the LDDstructure for the high voltages and used as the input/output stepcircuit and the n-channel MISFETs Qn having the LDD structure for thelow voltages and used as the peripheral circuits, the fabricationprocess comprises: the step of forming the individual gate insulatingfilm 26 and gate electrodes 27 of the n-channel MISFETs Qn for the highvoltages and the n-channel MISFETs Qn for the low voltages at a commonstep over the principal surface of the different active regions of thep⁻ -type well regions 22; the step of forming at a common step thelightly doped n-type semiconductor regions 29 for forming the LDDstructure in self-alignment with the individual gate electrodes 27 ofthe n-channel MISFETs Qn for the high voltages and the n-channel MISFETsQn for the low voltages over the principal surface portions of theindividual active regions of the p⁻ -type well regions 22; the step offorming the side wall spacers 31 at a common step on the side walls ofthe individual gate electrodes 27 of the n-channel MISFETs Qn for thehigh voltages and the n-channel MISFETs Qn for the low voltages; and thestep of forming the densely doped n⁺ -type semiconductor regions 32 inself-alignment with the side will spacers 31 over the individualprincipal surface portions of the active regions of the p⁻ -type wellregions 22 for forming the n-channel MISFETs Qn for the high voltagesand the n-channel MISFETs Qn for the low voltages. Thanks to thisconstruction, all the individual steps for forming the n-channel MISFETsQn for the high voltages and the n-channel MISFETs Qn for the lowvoltages can be shared to form the individual side wall spacers 31 atthe common step so that the number of steps of fabricating the DRAM 1can be reduced.

Interlayer Insulating Film Forming Step 1!

Next, the inter-layer insulating film 33 is formed all over the surfaceof the substrate including the surfaces of the aforementioned interlayerinsulating film 28 and side wall spacers 31. This inter-layer insulatingfilm 33 is used as an etching stopper layer when the individualelectrode layers of the information storing capacity elements C havingthe stacked structure are to be treated. The inter-layer insulating film33 is also used for electrically separating the lower electrode layers(35) of the information storing capacity elements C of the stackedstructure and the gate electrodes 27 and word lines 27 of the memorycell selecting MISFETs Qs individually. Moreover, the inter-layerinsulating film 33 is constructed to thicken the side wall spacers 31 ofthe p-channel MISFETs Qp. The inter-layer insulating film 33 is formedto have a thickness considering mainly the scrapes by the overetching ofthe upper conducting layer and by the cleaning step. The inter-layerinsulating film 33 is formed of a silicon oxide film which is depositedby the CVD method using inorganic silane gases and nitrogen oxide gasesas its source gases. In other words, this inter-layer insulating film 33can reduce the stress which is caused on the basis of the difference inthe coefficients of linear expansion between the dielectric film (36) ofthe information storing capacity elements C having the stacked structureand the underlying interlayer insulating film 28. The inter-layerinsulating film 33 is formed to have a thickness of about 130 to 180nm!, for example.

Next, as shown in FIG. 34, the inter-layer insulating film 33 isremoved, to form the connecting holes 33A and 34 individually, from then-type semiconductor regions 29 at the other (i.e., at the side wherethe lower lower electrode layers are connected) of the memory cellselecting MISFETs Qs for the memory cell M forming regions. Theconnecting holes 34 are formed in the regions which are defined by theside wall spacers 33B deposited on the side wall spacers 31 when theside wall spacers 31 and the interlayer insulating film 33 are etched.

Gate Wiring Line Forming Step 2!

Next, as shown in FIG. 35, all over the surface of the substrateincluding the upper surface of the interlayer insulating film 33, thereis deposited a polycrystalline silicon film which is formed with thelower lower electrode layers 35 of the information storing capacityelements C of the stacked structure of the memory cells M. Thispolycrystalline silicon film is partially connected with the n-typesemiconductor regions 29 through the aforementioned connecting holes 33Aand 34. The polycrystalline silicon film is formed of a polycrystallinesilicon film deposited by the CYD method, to have a thickness of about150 to 250 nm!. The polycrystalline silicon film is formed at the stepof forming the second-layer gate wiring lines of the fabricationprocess. After the deposition, the polycrystalline silicon film is dopedby the hot diffusion method with an n-type impurity such as P forreducing the resistance. This n-type impurity is diffused with a largeamount of n-type impurity through the aforementioned connecting holes34, but the n-type impurity is in such a low dope that it may not bediffused to the channel forming regions of the memory cell selectingMISFETs Qs.

Next, as shown in FIG. 36, another polycrystalline silicon film isdeposited on the aforementioned polycrystalline silicon film. This upperpolycrystalline silicon film is deposited by the CVD method to have athickness of about 250 to 350 nm!. The upper polycrystalline siliconfilm is doped after the deposition by the hot diffusion method with ann-type impurity such as P for reducing the resistance. This n-typeimpurity is densely introduced to improve the charge storage of theinformation storing capacity elements C having the stacked structure.

Next, as shown in FIG. 37, the polycrystalline silicon film of theaforementioned two-layered structure is treated into a predeterminedshape to form the lower electrode layer 35 by using the photolithographytechnology and the anisotropic etching technology. This photolithographytechnology includes the step of forming the etching mask (or thephotoresist film) and the step of removing the etching mask. Thisetching mask removing step is accomplished by the plasma treatment usingthe downstream of the mixed gases of freon gases (CHF₃) and oxygen gases(O₂). This treatment is effective for reducing the damages of theindividual elements of the DRAM 1.

Thus, in the DRAM 1 having its memory cells M constructed of a seriescircuit of the memory cell selecting MISFETs Qs and the informationstoring capacity elements C of the stacked structure, the lowerelectrode layers 35 to be connected with one of the n-type semiconductorregions 29 of the memory cell selecting MISFETs Qs of the informationstoring capacity elements C of the stacked structure is formed of thecomposite film in which the polycrystalline silicon film lightly dopedwith the n-type impurity for reducing the resistance and thepolycrystalline silicon film densely doped with the n-type impurity aresequentially laminated. Thanks to this construction, the lower electrodelayers 35 of the information storing capacity elements C of the stackedstructure of the memory cells M can be thickened to increase the area ofthe side walls of the lower electrode layers 35 in the verticaldirection so that the charge storage can be increased while reducing thearea of the memory cells M to improve the degree of integration. Sincethe surface of the polycrystalline silicon film over the lower electrodelayers 35 has a high impurity concentration, the amount of electriccharges can be increased to further improve the degree of integrationlikewise. Since, moreover, the impurity concentration of thepolycrystalline silicon film of the aforementioned lower electrodelayers 35 can be dropped to reduce the amount of diffusion of the n-typeimpurity to one of the n-type semiconductor regions 29 of the memorycell selecting MISFETs Qs, the short channel effect of the memory cellselecting MISFETs Qs can be reduced to shrink the area of the memorycells M thereby to further improve the degree of integration. Thepresent invention may be modified such that three or morepolycrystalline silicon films are deposited and are individually dopedwith the n-type impurity to form the aforementioned lower electrodelayers 35.

In the DRAM 1 having the memory cells M constructed of a series circuitof the memory cell selecting MISFETs Qs and the information storingcapacity elements C of the stacked structure, moreover, the fabricationprocess comprises: the step of introducing the n-type impurity forreducing the resistance into the first-layer polycrystalline siliconfilm after this first-layer polycrystalline silicon film has beendeposited all over the interlayer insulating film 33 of the p⁻ -typewell regions 22 including the surfaces of the memory cell selectingMISFETs Qs; the step of introducing the n-type impurity for reducing theresistance into the second-layer polycrystalline silicon film after thissecond-layer polycrystalline silicon film has been deposited all overthe first-layer polycrystalline silicon film; and the step of formingthe lower electrode layers 35 of the information storing capacityelements C of the stacked structure by anisotropically etching thesecond-layer polycrystalline silicon film and the first-layerpolycrystalline silicon film to subject them to the predeterminedpatterning. Thanks to this construction, even if the lower electrodelayers 35 of the information storing capacity elements C of the stackedstructure is thickened, the amount of the impurity introduced thereintocan be retained to some extent and homogenized. As a result, it ispossible to enhance the anisotropy of the anisotropical etching and toincrease the etching rate. Since the improvement in the anisotropy ofthe anisotropic etching can reduce the size of the lower electrodelayers 35, the area of the memory cells M can be shrunk to improve thedegree of integration of the DRAM 1.

Dielectric Film Forming Step!

Next, as shown in FIG. 38, the dielectric film 36 is formed all over thesubstrate including the surface of the lower electrode layers 35 of theinformation storing capacity elements C of the stacked structure of thememory cells M. This dielectric film 36 is formed of the two-layeredstructure in which the silicon nitride film 36A and the silicon oxidefilm 36B are basically laminated in the sequential manner, as has beendescribed hereinbefore. The lower silicon nitride film 36A is depositedby the CVD method, for example, to have a thickness of about 5 to 7 nm!.For forming this silicon nitride film 36A, the runaround of the oxygenis suppressed as much as possible. In case the silicon nitride film 36Ais formed over the lower electrode layers (i.e., the polycrystallinesilicon film) 35 at the ordinary production level, a natural siliconnitride film (although not shown) is formed between the lower electrodelayers 35 and the silicon nitride film 36A.

The upper silicon oxide film 36B of the aforementioned dielectric film36 is formed by subjecting the lower silicon nitride film 36A to ahigh-pressure oxidization method to have a thickness of about 1 to 3nm!. When the silicon oxide film 36B is formed, the lower siliconnitride film 36A has its thickness slightly reduced. The silicon oxidefilm 36B is basically formed in an oxygen gas atmosphere under apressure as high as 1.5 to 10 Torrs! and at a temperature as high as 800to 1,000 ° C.!. In the present embodiment, the silicon oxide film 36B isformed under a high pressure of 3 to 3.8 Torrs!, at an oxygen flow rate(of the source gases) of 2 1/min.! for oxidization, and at a hydrogenflow rate (of the source gases) of 3 to 8 1/min.!. The silicon oxidefilm 36B to be formed by the high-pressure oxidization method can bemade to have a desired thickness within a shorter time than that of thesilicon oxide film to be formed under a normal pressure (i.e., 1 Torr!).In short, the high-pressure oxidization method can shorten the heattreatment time at a high temperature so that it can reduce the pnjunction depth of the source regions and the drain regions of the memorycell selecting MISFETs Qs. The aforementioned natural silicon oxide filmcan be thinned if the run-around of the oxygen is reduced. Although thenumber of the fabrication steps is increased, on the other hand, thenatural silicon oxide film can be nitrized to form the dielectric film36 of the two-layered structure.

Gate Wiring Line Forming Step 3!

Next, a polycrystalline silicon film is deposited over the whole surfaceof the substrate including the dielectric film 36. The polycrystallinesilicon film is deposited by the CVD method to have a thickness of about80 to 120 nm!. This polycrystalline silicon film is formed at thethird-layer gate wiring line forming step of the fabrication process.After this, an n-type impurity such as P for reducing the resistance isintroduced into the polycrystalline silicon film by the hot diffusionmethod.

Next, the etching mask is formed over the aforementioned polycrystallinesilicon film all over the surface of the memory cell array 11E exceptingthe connected regions between one of the n-type semiconductor regions 29of the memory cell selecting MISFETs Qs and the complementary data lines(50). This etching mask is formed by the photoresist film using thephotolithography technology, for example. After this, as shown in FIG.39, the etching mask is used to sequentially etch the polycrystallinesilicon film and the dielectric film 36 anisotropically to form theupper electrode layer 37. By forming the upper electrode layer 37, theinformation storing capacity elements C of the stacked structure aresubstantially completed so that the memory cells M of the DRAM 1 arecompleted. After the completion of the memory cells M, theaforementioned etching mask is removed.

Next, as shown in FIG. 40, the hot oxidization treatment is accomplishedto form the insulating film (of the silicon oxide film) 38 is formedover the surface of the upper electrode layer 37. The step of formingthe insulating film 38 is to oxidize the etching residual (of thepolycrystalline silicon film) left on the underlying surface (i.e., thesurface of the interlayer insulating film 33) when the aforementionedupper electrode layer 37 is patterned. In the information storingcapacity elements C of the stacked structure, the two-layered lowerelectrode layer 35 and upper electrode layer 37 of the memory cellselecting MISFETs Qs are deposited. As a result, the stepped shape isenlarged at the connected portions especially between the complementarydata lines (50) and the memory cells M so that the etching residual isliable to be left. This etching residual shorts the complementary datalines (50) and the upper electrode layer 37.

In the DRAM 1 including the memory cells M constructed of the seriescircuit of the memory cell selecting MISFETs Qs having one of the n-typesemiconductor regions connected with the complementary data lines (50)and the information storing capacity elements C of the stacked structurein which the overlying lower electrode layer 35, dielectric film 36 andupper electrode layer 37 are sequentially laminated, the fabricationprocess comprises: the step of forming the upper electrode layer 37 bydepositing the polycrystalline silicon film by the CYD method over thedielectric film 36 of the aforementioned memory cells M and bysubjecting the polycrystalline silicon film to the predeterminedpatterning by the anisotropic etching; and the step of forming theinsulating film (of the silicon oxide film) 38 over the surface of theupper electrode layer 37 by the hot oxidization method. Thanks to thisconstruction, the etching residual of the polycrystalline silicon filmleft at the stepped portion of the underlying surface can be oxidizedafter the patterning of the polycrystalline silicon film by thesubsequent hot oxidizing step so that the upper electrode layer 37 andthe complementary data lines (50) can be prevented from being shorted toimprove the production yield.

Densely Doped Semiconductor Region Forming Step 2!

Next, in the regions for forming the p-channel MISFETs Qp of theaforementioned peripheral circuits, the interlayer insulating film 33formed at the aforementioned step is anisotropically etched to form theside wall spacers 33C, as shown in FIG. 41. These side wall spacers 33Care formed on the side walls of the aforementioned side wall spacers 31and in selfalignment with the aforementioned gate electrodes 27. Theside wall spacers 33C are formed to enlarge the gate length of the sidewall spacers 31 of the p-channel MISFETs Qp. The total gate length ofthe side wall spacers 31 and 33C is made to be about 200 nm!, as hasbeen described hereinbefore.

Next, a not-shown insulating film is formed all over the surface of thesubstrate including the surface of the upper electrode layer 37 of theinformation storing capacity elements C of the stacked structure, thesurface of the n-channel MISFETs Qn and the surface of the regionsforming the p-channel MISFETs Qp. This insulating film is used mainly asthe contamination preventing film when the impurity is introduced. Theinsulating film is formed of the silicon oxide film, which is depositedby the CVD method using inorganic silane gases and nitrogen oxide gases,for example, as its source gases, to have a small thickness of about 10nm!.

Next, a p-type impurity 39p is introduced, as shown in FIG. 42, into theregions forming the p-channel MISFETs Qp of the peripheral circuits.When this p-type impurity 39p is introduced, mainly the side wallspacers 31 and 33C are used as the impurity introduction mask. When thep-type impurity 39p is introduced, moreover, the regions to be formedwith the p-channel MISFETs Qp, namely, the regions to be formed with thememory cell arrays 11E and the n-channel MISFETs Qn are covered with thenot-shown impurity introduction mask (of the photoresist film). Theaforementioned p-type impurity 39p used is BF₂ (or B) having an impurityconcentration of about 10¹⁵ atoms/cm₂ !, for example, by the ionimplantation method of an energy of about 50 to 70 KeV!.

After this, a heat treatment is accomplished to elongate and diffuse theaforementioned p-type impurity 39p to form the p⁺ -type semiconductorregions 39. This heat treatment is accomplished at a temperature as highas about 900 to 1,000 ° C.!, for example, for 20 to 40 mdn.!. Thep-channel MISFETs Qp having the LDD structure are completed by formingthe p⁺ -type semiconductor regions 39. The p-channel MISFETs Qp enlargethe gate length of the side wall spacers 31 with the side wall spacers33C and are formed after the heat treatment (of the dielectric film 36,for example) for forming the information storing capacity element C ofthe stacked structure of the memory cells M. In short, the p-channelMISFETs Qp can reduce the diffusions of the p⁺ -type semiconductorregions 39 to the channel forming regions and the short channel effect.

Thus, in the DRAM 1 including the memory cells M having the seriescircuit of the memory cell selecting MISFETs Qs and the informationstoring capacity elements C of the stacked structure and thecomplementary MISFETs of the LDD structure constituting the peripheralcircuits, the fabrication process comprises: the step of sequentiallyforming the individual gate insulating film 26 and gate electrodes 27 ofthe memory cell selecting MISFETs Qs of the memory cells M and then-channel MISFETs Qn and the p-channel MISFETs Qp of the peripheralcircuits; the step of forming the individual lightly doped n-typesemiconductor regions 29 and p-type semiconductor regions 30 for formingthe LDD structures of the memory cell selecting MISFETs Qs, then-channel MISFETs Qn and the p-channel MISFETs Qp in self-alignment withthe gate electrodes 27; the step of forming the side wall spacers 31 onthe side walls of the individual gate electrodes 27 of the memory cellselecting MISFETs Qs, the n-channel MISFETs Qn and the p-channel MISFETsQp; the step of forming the densely doped n⁺ -type semiconductor regions32 of the n-channel MISFETs Qn in self-alignment of the side wallspacers 31; the step of forming the information storing capacityelements C of the stacked structure of the memory cells M; the step offorming the side wall spacers 33C on the side walls of the gateelectrodes 27 of the p-channel MISFETs Qp through the aforementionedside wall spacers 31 in self-alignment with the gate electrodes 27; andthe step of forming the densely doped p⁺ -type semiconductor regions 39of the p-channel MISFETs Qp in self-alignment with the side wall spacers33C. Thanks to this construction, the n-channel MISFETs Qn regulates thegate length of the lightly doped n-type semiconductor regions 29 forforming the LDD structure with the single-layered side wall spacers 31so that they can shorten the gate length of the n-type semiconductorregions 29. The p-channel MISFETs Qp regulates the runabout of thedensely doped p⁺ -type semiconductor regions 39 to the channel formingregions with the multi-layered side wall spacers 31 and 33C, and thedensely doped p⁺ -type semiconductor regions 39 is formed after the heattreatment for forming the information storage capacity elements C of thestacked structure of the memory cells M. As a result, it is possible tofurther reduce the runabout of the p⁺ -type semiconductor regions 39 tothe channel forming regions.

The fabrication process further comprises the step of forming theinterlayer insulating films 33 after the step of forming the denselydoped n⁺ -type semiconductor regions 32 of the n-channel MISFETs Qn andbefore the step of forming the information storing capacity elements Cof the stacked structure of the memory cells M. After the interlayerinsulating film 33 have been formed, the aforementioned side wallspacers 33C are formed by making use of the aforementioned interlayerinsulating film 33. Thanks to this construction, the step of forming theside wall spacers 33C can be partially (for depositing the film) sharedby the step of forming the interlayer insulating film 33. As a result,the number of fabrication steps of the DRAM 1 can be reduced to anextent corresponding to that share.

Interlayer Insulating Film Forming Step 2!

Next, an interlayer insulating film 40 is formed all over the surface ofthe substrate including the individual elements of the aforementionedDRAM 1. This interlayer insulating film 40 is formed of the siliconoxide film which is deposited by the CVD method using inorganic silanegases and nitrogen oxide gases, for example, as its source gases. Theinterlayer insulating film 40 is formed to have a thickness of about 250to 350 nm!, for example.

Next, as shown in FIG. 43, the interlayer insulating film 40 is formedwith the connecting holes 40A at the connected portions between thememory cells M and the complementary data lines 50. These connectingholes 40 A are formed by the anisotropic etching, for example.

Gate Wiring Line Forming Step 4!

Next, as shown in FIG. 44, there are formed the complementary data lines(DL) 50 which are connected with one of the n-type semiconductor regions29 of the memory cell selecting MISFETs Qs through the aforementionedconnecting holes 40 A and which are extended over the interlayerinsulating film 40 . The complementary data lines 50 are formed at thefourthlayer gate wiring line forming step of the fabrication process.The complementary data lines 50 are constructed of the two-layeredstructure in which the polycrystalline silicon film 50A and thecomplementary data lines 50 are sequentially laminated. The lowerpolycrystalline silicon film 50A are deposited by the CVD method to havea thickness of about 80 to 120 nm!, for example. The polycrystallinesilicon film 50A are doped after the deposition with an n-type impuritysuch as P by the hot oxidization method. The polycrystalline siliconfilm 50A thus deposited by the CVD method has a high step coverage atthe stepped portions of the connecting holes 40A so that they can reducethe defects such as the disconnections of the complementary data lines50. In case the connecting holes 40A are partially superposed over theelement separating insulating film 23 in the connected portions betweenthe memory cells M and the complementary data lines 50 due to themasking misalignment at the step of forming the connecting holes 40A andthe element separating insulating film 23, the n-type impurity can bediffused from the polycrystalline silicon film 50A to the principalsurface portions of the p⁻ -type well regions 22 to connect the n-typesemiconductor regions 29 and the complementary data lines 50 so thatthey can prevent the complementary data lines 50 and the p⁻ -type wellregions 22 from being shorted. The upper transition-metal silicide film50B is made of the WSi₂ film, which is deposited by the CYD method, forexample, to have a thickness of 100 to 200 nm!, for example. This uppertransition-metal silicide film 50B is formed mainly to reduce theresistance of the complementary data lines 50 and to increase theindividual speeds of the information writing operations and theinformation reading operations. Since, moreover, the uppertransition-metal silicide film 50B is deposited by the CVD method, itcan further reduce the defects such as the disconnections of thecomplementary data lines 50.

These complementary data lines 50 are formed by patterning theindividual deposited upper transitionmetal silicide film SOB into apredetermined shape by the anisotropic etching, for example.

Interlayer Insulating Film Forming Step 3!

Next, all the surface of the substrate including the complementary datalines 50 is formed with the interlayer insulating film 51. Thisinterlayer insulating film 51 is formed of the two-layered structure inwhich the silicon oxide film 51A and the BPSG film 51B are sequentiallylaminated. The lower silicon oxide film 51A is deposited by the CVDmethod using inorganic silane gases and nitrogen oxide gases, forexample, as its source gases, to have a thickness of about 100 to 200nm!. The lower silicon oxide film 51A is formed to prevent the leakageof the impurities (e.g., P and B) of the upper BPSG film 51B. This upperBPSG film 51B is deposited by the CVD method, for example, to have athickness of about 250 to 350 nm!. The BPSG film 51B is subjected to theflowing treatment in the atmosphere of the nitrogen oxide gases at atemperature equal to or higher than about 800 ° C.!.

Next, as shown in FIG. 45, the aforementioned interlayer insulating film51 is formed with the connecting holes 51C. These connecting holes 51Care formed by removing the overlying interlayer insulating film 51 fromthe n⁺ -type semiconductor regions 32 and the p⁺ -type semiconductorregions 39 of the individual elements of the DRAM 1, the not-shownwiring lines 50 and the upper electrode layer 37. The connecting holes51c are formed by the anisotropic etching, for example.

In the regions forming the aforementioned p-channel MISFETs Qp,moreover, the p⁺ -type semiconductor regions 39 have a large diffusioncoefficient of the p-type impurity so that the surface impurityconcentration is lower than that of the n⁺ -type semiconductor regions32. Moreover, the n⁺ -type semiconductor regions 32 is etched at itssurface of high impurity concentration overetched when theaforementioned connecting holes 51C are formed, so that its surfaceimpurity concentration is further dropped. Still moreover, the p⁺ -typesemiconductor regions 39 has a larger work function difference than thatof the n⁺ -type semiconductor regions 32 because the wiring lines to beconnected therewith are formed of the transition-metal (e.g., W) film.In the regions defined by the connecting holes 51C, therefore, thep-channel MISFETs Qp may have the surfaces of the p⁺ -type semiconductorregions 39 doped with a p-type impurity to increase the impurityconcentration of the surfaces of the p⁺ -type semiconductor regions 39.Thanks to this construction, the connection resistance between the p⁺-type semiconductor regions 39 of the p-channel MISFETs Qp and thewiring lines (52) can be reduced.

Wiring Line Forming Step 1!

Next, as shown in FIG. 46, the wiring lines (including the column selectsignal lines) 52 are so formed over the interlayer insulating film 51 asto connect the n⁺ -type semiconductor regions 32 and the p⁺ -typesemiconductor regions 39 through the aforementioned connecting holes51C. The wiring lines 52 are formed of the transition-metal film, e.g.,the W film deposited by the sputtering method, to have a thickness ofabout 350 to 450 nm!, for example. The wiring lines 52 can be formed bypatterning them in a predetermined shape by the anisotropic etching, forexample, after they have been deposited all over the surface of theinterlayer insulating film 51.

Interlayer Insulating Film Forming Step 4!

Next, as shown in FIG. 47, all the surface of the substrate includingthe aforementioned wiring lines 52 is formed thereover with theinterlayer insulating film 53. This interlayer insulating film 53 isformed of the three-layered structure, in which the silicon oxide film(i.e., the deposited type insulating film) 53A, the silicon oxide film(i.e., the applied type insulating film) 53B and the silicon oxide film(i.e., the deposited type insulating film) 53C are sequentiallylaminated. The lower silicon oxide film 53A is deposited by the C-CVDmethod using tetraethoxysilane gases as its source gases, to have athickness of about 250 to 350 nm!. The intermediate silicon oxide film53B is formed to flatten the surface of the interlayer insulating film53. This silicon oxide film 53B is formed by several (two to five) timesof applications (to have a total film thickness of about 100 to 150 nm!by the 50G method, by a subsequent baking treatment (at about 450 ° C.!)and by retarding the surface by the etching. As a result of theretardation by this etching, the silicon oxide film 53B is formed onlyin the recesses of the stepped shape of the surface of the lower siliconoxide film 53A. On the other hand, the intermediate layer of theinter-layer insulating film 53 may be formed of an organic film such asa polyimide resin film in place of the aforementioned silicon oxide film53B. In order to enhance the strength of the interlayer insulating film53 as a whole, the upper silicon oxide film 53C is deposited by theC-CVD method using tetraethoxysilane gases, for example, as its sourcegases, to have a thickness of about 250 to 350 nm!.

Next, the predetermined wiring lines 52 of the aforementioned interlayerinsulating film are removed to form the connecting holes 53D. Theseconnecting holes 53D are formed by the anisotropic etching, for example.

Next, the transition-metal film 54 is laminated (or buried) on thesurface of the wiring lines 52 which are exposed to the insides of theconnecting holes 53D. The transition-metal film 54 is formed of a W filmdeposited by the selective CYD method, for example, to have a thicknessof about 600 to 800 nm!. This W film has the following reaction formula:

650-700° C.

    WF.sub.6 +3SiCl.sub.2 H.sub.2 →WSi.sub.2 +HCl+SiF.sub.4 +F.sub.2.

Wiring Line Forming Step 2!

Next, as shown in FIG. 49, the wiring lines (including the shunting wordlines) 55 are so formed over the interlayer insulating film 53 that theymay be connected with the transition-metal film 54 buried in theaforementioned connecting holes 53D. These shunting word lines 55 areformed of the two-layered structure in which the transition-metalnitride film (or the transition-metal film) 55A and the aluminum alloyfilm 55B are sequentially laminated. The lower transition-metal nitridefilm 55A is formed of a TiN film deposited by the sputtering method, forexample, to have a thickness of about 130 to 180 nm!. Thetransition-metal nitride film 55A is formed to prevent the deposition ofthe Si and the alloying reaction with the aluminum at the portions ofthe aforementioned connecting holes 53D, as has been describedhereinbefore. The upper aluminum alloy film 55B is deposited by thesputtering method, for example, to have a thickness of about 600 to 800nm!. The wiring lines 55 can be formed by laminating the lowertransitionmetal nitride film 55A and the upper aluminum alloy film 55Bsequentially and then by patterning lamination into a predeterminedshape by the anisotropic etching, for example.

Passivation Film Forming Step!

Next, as shown in FIG. 1, all the surface of the substrate including theaforementioned wiring lines 55 is formed thereover with the passivationfilm 56. This passivation film 56 is formed of the composite film inwhich the silicon oxide film 56A and the silicon nitride film 56B aresequentially laminated, as has been described hereinbefore. The lowersilicon oxide film 56A is deposited by the C-CVD method using thetetraethoxysilane gases as its source gases, as has been describedhereinbefore. The upper silicon nitride film 56B is deposited by theplasma CVD method.

Incidentally, although not shown in FIG. 1, a resin film is applied tothe upper surface of the passivation film 56. This resin film is formedto improve the α-ray soft error withstand voltage. This resin film isformed of a polyimide resin film, which is applied by a pottingtechnology (including the dropping application step, the baking step andthe patterning step of the resin), for example, to have a thickness ofabout 8 to 12 μm!. The resin film is basically applied to the wholesurface of the DRAM 1 excepting the regions which are opened tocorrespond to the external terminals. Moreover, the resin film may bedivided in plurality and arranged over the surface of the DRAM 1. Inother words, the resin film is arranged in the regions, which aredesired to retain the α-ray soft error withstand voltage of the DRAM 1,such as the memory cell arrays 11E and the portions (12 and 13) of thedirect peripheral circuits but not in the indirect peripheral circuitsand the remaining portions of the direct peripheral circuits so that theregions left unarranged may be used as the divided ones. By thusdividing the resin film, the stress of the resin film can be reduced toprevent the cracking of the passivation film.

Fuse Opening Step!

On the other hand, the aforementioned DRAM 1 is arranged with theY-redundancy circuit 1812 and the X-redundancy circuit 1806 forrelieving the defective complementary data lines (DL) 50, the defectiveword lines (WL) 27 (or the shunting word lines 55). The Y-redundancycircuit 1812 accomplishes the switching from the defective complementarydata lines 50 to the redundancy complementary data lines 50 independence upon whether or not a fuse element F is to be cut. Likewise,the X-redundancy circuit 1806 accomplishes the switching from thedefective word lines 27 to the redundancy word lines 27 in dependenceupon whether or not the fuse element F is to be cut.

This fuse element F is formed of a conducting layer shared with thecomplementary data lines 50 and the wiring lines 50, as shown in FIG. 50(presenting a section showing an essential portion). Since the DRAM 1 ofthe present embodiment adopts the laser cutting method, the fuse element50 is cut with the laser beam. Since this fuse element 50 has anunstable cutting in the presence of a thick passivation film 56, thereis provided over the fuse element 50 a fuse opening 56C which is formedin the passivation film 56. Since the etching gases to be used forforming the fuse opening 56C is also used for etching the fuse element50, there is left over the fuse element 50 an insulating film having asuitable thickness (no more than 800 nm!) such as the interlayerinsulating film 51 and the interlayer insulating film 53. The conductinglayer below the fuse element 50 such as the same conducting layer as theupper electrode layer 37 of the information storing capacity elements Cof the stacked structure is too thin and highly resistive to suit thefuse element F. Moreover, the same conducting layers as the lowerelectrode layer 35 and the gate electrodes 27 are overlaid by a numberof insulating films so that the steps of forming the fuse opening areincreased and complicated. Since, moreover, the conducting layersidentical to the wiring lines 52 and 55 over the fuse element 50 haveproperties to reflect the laser beam, they are not suitable for the fuseelement F.

The method of forming the fuse element 50 and the fuse opening 56C willbe briefly described with reference to FIGS. 51 to 53 (presentingsections showing the essential portion at the individual fabricationsteps).

First of all, as shown in FIG. 51, the fuse element 50 is formed at thesame fabricating step as that of the complementary data lines 50 overthe regions of the interlayer insulating film 40 for forming the fuseelement F.

Next, the interlayer insulating films 51 (or 51A and SIB) are formed,and the wiring lines 52 are then formed, as shown in FIG. 52. No wiringline 52 is present over the fuse element 50, as shown in FIG. 52.

Next, the interlayer insulating films 53 (or 53A, 53B and 53C) areformed, and the wiring lines 55 are then formed, as shown in FIG. 53. Nowiring line 55 is present over the aforementioned fuse element 50.

Next, the passivation film 56 is formed, and the fuse opening 56C isformed in the passivation film 56 over the fuse element 50, as shown inFIG. 50. This fuse opening 56C can be formed, although not described, atthe fabrication step shared with that of opening the (bonding) portionin which the external terminals BP of the passivation film 56 arepresent.

Thus, in the DRAM 1 including: the memory cells M formed of the seriescircuit of the memory cell selecting MISFETs Qs and the informationstoring capacity elements C of the stacked structure at theintersections between the complementary data lines 50 and the word lines27; and the laser cutting redundancy fuse element 50 for relieving thedefective ones of the complementary data lines 50 and the word lines,the complementary data lines 50 are formed of the composite film, inwhich the polycrystalline silicon film 50A and the transition-metalsilicide film 50B deposited by the CVD method are sequentiallylaminated, the laser cutting redundancy fuse element 50 is formed of theconducting layer shared with the complementary data lines 50. Thanks tothis construction, the complementary data lines 50 are formed over thememory cell selecting MISFETs Qs of the aforementioned memory cells Mand the information storing capacity elements C of the stackedstructure. As a result, the number of the insulating films over thelaser cutting redundancy fuse element 50 can be reduced to simplify theprocess of opening the insulating films over the laser cuttingredundancy fuse element 50. At the same time, the composite film formedof the polycrystalline silicon film 50A and the transition-metalsilicide film 50B has a higher absorptivity of the laser beam than thoseof the wiring lines 52 and 55 formed over the complementary data lines50. As a result, the laser cutting redundancy fuse element 50 can be cutsimply and reliably.

The DRAM 1 of the present embodiment is completed by a series of stepsfor forming and opening the aforementioned passivation film 56.

Next, in the fabrication process of the DRAM 1, the steps of fabricatingthe individual essential portions will be described in detail in thefollowing.

Wiring Line & Connecting Hole Forming Steps!

In the fabrication process of the DRAM 1, the complementary data lines(DL) 50, the wiring lines 52, the wiring lines 55 and the connectingholes 40A, 51C and 53D are basically and individually treated by thephotolithography technology using a multi-layered resist mask. Thismulti-layered resist mask is formed of a three-layered structure, forexample, in which an inphotosensitive resin film (e.g., an organic filmsuch as a polyimide resin film), an intermediate film (e.g., aninorganic film such as a silicon oxide film applied by the SOG method)and a photosensitive resin film are sequentially laminated.

The multi-layered resist mask is used to damp the stepped shape-growingby the multi-layered structure mainly with the lower film and theintermediate film and to improve the treating accuracy of the upperphotosensitive resin film and the treating accuracy of the material tobe etched. The multi-layered resist mask is formed by the followingmethod.

First of all, the inphotosensitive resin film, the intermediate film andthe photosensitive resin film are sequentially laminated over thesurface of the material to be etched (e.g., the aforementionedcomplementary data lines 50) to form the multi-layered resist film.

Next, the upper photosensitive resin film of the multi-layered resinfilm is treated by the ordinary exposure and development to form anetching mask.

Next, this etching mask is used to pattern the intermediate film andinphotosensitive resin film of the multi-layered resist filmsequentially by the anisotropic etching to form the multi-layered resistmask. In this patterning, the lower inphotosensitive resin film ispatterned by the anisotropic technology using oxygen (O₂) gases andhalogen (e.g., Cl₂ or Br₂) gases. The etching apparatus used isexemplified by the reactive ion etching (i.e., RIE) apparatus, themagnetron type RIE apparatus or the μ-wave ECR apparatus. The etchingpressure used is about 1 to 10 mTorrs!, and the high-frequency outputused is about 0.25 to 30 /cm² !. On the other hand, the halogen gasesused in the aforementioned anisotropic etching are not the halogen gases(which are produced together with halogen compounds) as the out gases ofa solid such as vinyl chloride but are supplied from the outside of avacuum chamber by placing the vinyl chloride in the vacuum chamber.

The anisotropic gases of the aforementioned oxygen gases and the halogengases will produce carboxylic acid, if the lower inphotosensitive resinfilm is etched with the oxygen gases, so that an acid chloride having alower vapor pressure is produced if the halogen gases are added to thatcarboxylic acid. As a result, the produced gases can be easily relievedto reduce the amount of the side etching of the lower inphotosensitiveresin film.

Thus, the multi-layered resist film is formed to have the three layers,of which the lower inphotosensitive resin film if patterned by theanisotropic etching using the oxygen gases and the halogen gases. Thanksto this construction, the anisotropic etching gases used are the halogengases so that the side etching amount of the lower inphotosensitiveresin film can be reduced to improve the treating accuracy. At the sametime, any halogen compound (e.g., CF₄ or CCl₄) is used as theanisotropic etching gases so that any organic substance can be preventedfrom sticking to the patterned sides of the lower inphotosensitive resinfilm. Thanks to this prevention, the removing step of the organicsubstance can be reduced together with the contaminations of the innerwalls of the vacuum chamber of the etching apparatus. Moreover, thecontaminations of the vacuum chamber inner walls can be reduced togetherwith the repeated sticks of the organic substances which may drop fromthe aforementioned inner walls onto the surface of the semiconductorwafer being fabricated, so that the production yield can be improved.

Since, moreover, the halogen compound such as carbon (C) is not used asthe anisotropic etching gases, the anisotropic etching rate can beincreased.

In this anisotropic etching, still moreover, not the halogen gases asthe solid out gases but the pure halogen gases coming from the outsideof the vacuum chamber are used so that similar effects can be achieved.

Wiring Line Forming Step 1!

In the fabrication process of the aforementioned RAM 1, the treatingaccuracy of the wiring lines 52, i.e., the W film can be improved byadopting the cold anisotropic etching.

The anisotropic etching of the wiring lines 52 is accomplished in thevacuum chamber of the RIE apparatus or the like. This vacuum chamber isevacuated under a vacuum within about 10⁻² to 10⁻³ Torrs!, in which theanisotropic etching is accomplished. As shown in FIG. 54 (presenting arelation between the temperature and vacuum pressure of tungstenhexafluoride WF₆), the WF₆ has its vacuum pressure dropped to or near 0mTorrs! against the degree of vacuum in the vacuum chamber at a lowtemperature equal to or lower than about -40 ° C.!. More specifically,the wiring lines 52 can have their etching anisotropy improved, becausethe ions will impinge, as a result of the anisotropic etching at theabove-specified low temperature range, upon not the treated side wallsbut the bottom being treated so that they are evaporated. As a result,it is possible to improve the treating accuracy of the wiring lines 52.

Connecting Hole Forming Step!

In the fabrication process of the aforementioned DRAM 1, theaforementioned connecting holes 51C (or 53D) can be individually formedinto a taper shape by making use of the magnetron RIE apparatus or theμ-wave ECR apparatus.

The connecting holes 51C can control their taper angle (i.e., their stepangle) by controlling the etching pressure, the etching gas flow rate orthe high-frequency output of the etching conditions. In order to controlthe above-specified taper angle without deteriorating the etchingperformance, it is desirable to control the etching pressure or theetching gas flow rate. The etching rate of the anisotropic etching isdetermined by the product of the ion current and the mean ion energy,and the taper angle is determined by the mean ion energy for a constantion current. On the other hand, this ion current has a tendency to beproportional to the high-frequency output and adversely proportional tothe voltage Vdc between the semiconductor wafer (or electrodes) and theplasma in case the high-frequency output is constant.

As seen from a relation between the etching pressure and the energy inFIG. 55(A), the anisotropic etching using the RIE apparatus has a narrowstable discharge region against the etching pressure, a steep change ofthe voltage Vdc, and a steep change of the mean ion energy. In otherwords, the controllability of the taper angle is not good.

As seen from a relation between the etching pressure and the energy inFIG. 55(B), on the contrary, the anisotropic etching using the magnetronRIE apparatus (or the μ-wave ECR apparatus) has a more ion amount by 1to 2 orders so that the stable discharge region against the etchingpressure is widened. As seen from a relation between the ion energy andthe etching rate in FIG. 55(C) and from a relation between the ionenergy and the taper angle in FIG. 55(D), therefore, the controllabilityof the taper angle is enhanced. The etching rate of the stepped portionis one which is determined by the ion energy corresponding to cos θtimes as high as that of the flat portion. This means that the ioncurrent density of the stepped portion of the taper angle cos θ times ashigh as that of the flat portion. Incidentally, as the taper angle θcomes the closer to 90 degrees, the stepped portion of the connectingholes grows the steeper. As the taper angle e comes the closer to 0degrees, the stepped portions grow the gentler.

Thus, the connecting holes 51C are formed by the anisotropic etchingusing the magnetron RIE apparatus (or the μ-wave ECR apparatus) so thatthe stable discharge region against the etching pressure can be widenedto reduce the individual changes of the voltage Vdc and the mean ionenergy. As a result, the controllability of the taper angle can beimproved without deteriorating the etching performance. In short, thetaper angle can be simply decided without any dispersion to 60 to 80degrees, as shown in FIG. 55(D). As a result, the connecting holes 51Ccan be tapered to reduce the defects such as the disconnections of thewiring lines 52 at the stepped portions of the connecting holes 51C.Incidentally, there arises no problem in the present embodiment becausethe transition-metal film 54 is buried in the connecting holes 53D.Otherwise, however, similar tapers are formed.

Connecting Hole Forming Step!

In the fabrication process of the aforementioned DRAM 1, the insulatingfilm such as the aforementioned connecting holes 51C and 53D is treatedby the cold anisotropic etching.

First of all, the DRAM 1 (i.e., the semiconductor wafer to be diced) isdirectly attracted to the lower electrodes in the vacuum chamber of theetching apparatus by an interposed electrostatic attracting plate. Thelower electrodes are cooled at all times so that the semiconductor waferis held at normal or lower temperatures. In this state, the interlayerinsulating films 51 and 53 are individually anisotropically etched toform the connecting holes 51C and 53D.

Since the anisotropic etching gases (i.e., the halogen compound CHF₃)are deposited more on the surface of the semiconductor wafer at a lowertemperature than that of the inner walls of the etching chamber. As aresult, the adoption of this cold anisotropic etching can reduce theflow rate of the above-specified anisotropic etching gases and reducethe contaminations of the inner walls of the vacuum chamber.

(Embodiment II)

The present embodiment II is a second embodiment of the presentinvention, which adopts the leaf type in the step of burying thetransition-metal film in the connecting holes for connecting thedifferent wiring layers, so as to improve the production yield of theDRAM 1 of the foregoing embodiment I.

An essential portion of the DRAM 1 according to the embodiment II of thepresent invention is shown in FIG. 56 (presenting the essential portionin section).

In the DRAM 1, as shown in FIG. 56, a transition-metal film 83 buried ina connecting hole 82A formed in an interlayer insulating film 82 isconnected with a wiring line 81 formed over an under insulating film 80.The wiring line 81 is formed of an aluminum film or its alloy film. Theinterlayer insulating film 82 is formed of either a single layer of asilicon oxide film or a composite composed mainly of the former. Thetransition-metal film 83 buried in the connecting hole 82A is formed ofthe W film which is deposited by the selective CVD method. Thistransition-metal film 83 is connected with a not-shown wiring line whichextends over the interlayer insulating film 82.

The structure shown in FIG. 56 can be formed by the fabrication methodusing the following leaf type.

First of all, the connecting hole 82A is formed in the interlayerinsulating film 82, and the wiring line 81 has its surface exposed tothe inside of the connecting hole 82A. The surface of this wiring line81 thus exposed is oxidized to form alumina (Al₂ O₃).

Next, the alumina thus formed over the aforementioned wiring line 81 isremoved by the sputtering method. This puttering method uses the mixedgases of argon (Ar) gases and fluorine group (NF₃, XeF, CF₄ or CHF₃)gases. The aforementioned argon gases can remove the alumina, which isformed over the wiring line 81, by the sputtering with their argon ions.The fluorine group gases can promote the sputtering rate of the alumina.Moreover, the fluorine group gases remove the uncoupled layer, which isformed over the interlayer insulating film 82 as a result of thecollisions of the argon ions, to improve the selectivity of thetransition-metal film 83 while protecting the surface of the wiring line81 against the corrosion. More specifically, only the argon gases wouldform the uncoupled hands on the surface of the interlayer insulatingfilm 82 to lose the selectivity of the transition-metal film 83. Incase, however, a halogen compound such as Cl₂ were mixed in the argongases, the uncoupled layer could be removed, but the surface of the 81would be corroded. Therefore, the sputtering method uses the mixed gasesof the argon gases and the fluorine group gases, as has been describedhereinbefore.

Next, the transition-metal film 83 is selectively deposited over thewiring line 81 in the aforementioned connecting hole 82A so that it isburied in the connecting hole 82A.

Thus, since the alumina is removed from the surface of the wiring line81 by the sputtering method using the aforementioned mixed gases, it ispossible to connect the wiring line 81 and the transition-metal film 83excellently and to retain the selectivity of the transition-metal film83.

As shown in FIG. 56, moreover, the fluorine (F) used in the sputteringmethod sputters the surface of the wiring line 81 to hit away thealuminum particles. These aluminum particles stick to the inner walls ofthe connecting hole 82A to form a cross contamination 81A. This crosscontamination 81A gives a higher deposition rate to the transition-metalfilm 83 than that of the surface of the interlayer insulating film 82 sothat the upper portion of the transition-metal film 83 is protruded fromthe surface of the interlayer insulating film 82. This protrusion of thetransition-metal film 83 drops the treating accuracy of an upper wiringline to be connected therewith.

In order to reduce the protrusion of the transition-metal film 83, theDRAM 1 shown in FIG. 57 (presenting an essential portion in section) hasits cross contamination 81A left as it is but is formed with a taperportion 82B at the upper portion of the connecting hole 82A. This taperportion 82B can be formed by an isotropic etching. The connecting hole82A can be formed by an anisotropic etching. Specifically, the taperportion 82B can remove an upper portion of the cross contamination 81Ato expose the surface of the interlayer insulating film 82 and to dropthe deposition rate of the transition-metal film 83 at that portionthereby to prevent the protrusion of the transition-metal film 83.Since, on the contrary, the deposition rate of the transition-metal film83 can be increased by leaving the cross contamination 81A, thefabrication time can be shortened.

In the DRAM 1 shown in FIG. 58 (presenting an essential portion insection), on the other hand, the cross contamination 81A is positivelyformed on the inner wall of the aforementioned connecting hole 82A toaccelerate the deposition rate of the transition-metal film 83.

Although the deposition rate of the transition-metal film 83 is slightlyretarded, the cross contamination 81A may be removed substantiallywholly to give a complete taper to the connecting hole 82A.

Thanks to the adoption of the leaf type, moreover, the controllabilityof the thickness of the aforementioned transition-metal film 83 can beimproved better than that of the batch type.

(Embodiment III)

The present embodiment III is directed to a third embodiment of thepresent invention, in which the transition-metal film is buried in theconnecting hole for connecting the semiconductor substrate and thewiring layer, although having different a structure from that of theDRAM 1 of the foregoing embodiment II, and in which the leaf type isadopted in the burying step.

An essential portion of the DRAM 1 according to the embodiment III ofthe present invention is shown in FIG. 59 (presenting the essentialportion in section).

In the DRAM 1 of the present embodiment III, as shown in FIG. 59, withthe n⁺ -type semiconductor region 32 formed over in the principalportion of the p⁺ -type well region 22, there is connected atransition-metal film 84 which is buried in the connecting hole 80Aformed in the interlayer insulating film 80. The n⁺ -type semiconductorregion 32 is made of silicon (Si), as has been described in connectionwith the foregoing embodiment I. The interlayer insulating film 80 isformed of either a single layer of a silicon oxide film or a compositefilm made mainly of the former. The transition-metal film 84 buried inthe connecting hole 80A is formed of the composite film, in which a Wfilm 84A deposited by the selective CVD method using the siliconreducing reaction (i.e., the reaction between the Si of the n⁺ -typesemiconductor region 32 and WF₆) and a W film deposited by the selectiveCVD method using a silane reducing reaction (i.e., the reaction betweenSiH₄ and WF₆) are sequentially laminated. The lower W film 84A isprepared by the silicon reducing reaction so that it can improve thecontactness between the n⁺ -type semiconductor region 32 and thetransition-metal film 84. The upper W film 84B is prepared by the silanereducing reaction so that it can reduce the amount of reduction of thesurface of the n⁺ -type semiconductor region 32 thereby to form the n⁺-type semiconductor region 32 having a small pn junction depth. Thetransition-metal film 84 has its upper portion connected with the wiringline (e.g., the aluminum alloy film) 81 extending over the interlayerinsulating film 80.

In the structure shown in FIG. 59, if the upper W film 84B is depositedafter lapse of a short time from the formation of the lower W film 84Aat the step forming the transition-metal film 84 deposited in theaforementioned connecting hole 80A, they are separated at theirinterface (as indicated at numeral 84C). This separation is causedbecause the upper W film 84B has a higher stress than that of the lowerW film 84A. On the other hand, this separation is also caused in casereaction by-products such as fluorine group gases are present.

In the DRAM 1 shown in FIG. 60 (presenting an essential portion insection, the lower W film 84A and the upper W film 84B of theaforementioned transition-metal film 84 are continuously formed so thatthey are prevented from being separated at their interface. The methodof continuously forming the lower W film 84A and the higher W film 84Bof the transition-metal film 84 will be described in the following.

First of all, in the selective CVD method adopting the leaf type, asshown in FIG. 61(A), the WF₆ is supplied as the source gases to thereaction chamber of the CVD apparatus, as plotted the relation betweenthe deposition time of the W film and the source gas flow rate. The WF₆reacts with the Si at the surface of the n⁺ -type semiconductor region32 exposed to the inside of the connecting hole 80A, as shown in FIG.60, to form the lower W film 84A. With supply of the WF₆, as shown inFIG. 61(B), a relation between the deposition time and the amount of thereaction by-products (F₂, SiF₃ and SiF₄) is monitored. This amount ofthe reaction by-products can be monitored by either a gas massspectrometer (i.e,. a gas mass analyzer) arranged in the exhaust gassupply tube from the reaction chamber or a plasma emission monitorarranged in the reaction chamber (i.e,. the chamber).

Next, when the lower W film 84A is formed, the Si of the surface of then⁺ -type semiconductor region 32 is not exposed so that the depositionof the W film is automatically stopped. As shown at (A) and (B) in FIG.61, however, the silane gases are supplied to the reaction chamberbefore the end of the aforementioned silicon reducing reaction from thereduction in the amount of the reaction by-products to deposit the upperW film 84B. In short, the reaction is changed from the silicon reducingreaction to the silane reducing reaction to form the lower W film 84Aand the upper W film 84B continuously and sequentially.

Thus, the lower W film 84A and the upper W film 84B of theaforementioned transition-metal film 84 can be continuously formed toprevent the separations at their interface.

Thanks to the adoption of the leaf type, moreover, the controllabilityof the thickness of the transition-metal film 84 can be improved betterthan that of the batch type.

(Embodiment IV)

The present embodiment IV is directed to a fourth embodiment of thepresent invention describing the suitable method of forming thedielectric film 36 and the apparatus for executing the process in theinformation storing capacity element C of the stacked structure of thememory cell M of the DRAM 1 of the foregoing embodiment I.

The leaf type CVD apparatus according to the embodiment IV of thepresent invention is shown in FIG. 62.

As shown in FIG. 62, the leaf type CVD apparatus is constructed mainlyof a load/unload chamber 90, a transfer chamber 91, a pretreatingchamber 92, a first reactor chamber 93 and a second reactor chamber 94.These treating chambers 90 to 94 are connected through gate valves 96.

The load/unload chamber 90 is so constructed that a cassette cassette90A accommodating a plurality of semiconductor wafers 100 may beremovably attached thereto. This load/unload chamber 90 supplies thesemiconductor wafers 100 untreated to the transfer chamber 91 andaccommodates the semiconductor wafers 100 treated from the transferchamber 91.

This transfer chamber 91 is so constructed that the untreatedsemiconductor wafers 100 may be supplied to the individual pretreatingchambers 92 and 93 and that the treated semiconductor wafers 100 may beextracted from the pretreating chambers 92 and 93. As shown in FIG. 63(presenting an essential portion schematically), the supply and take-outof the semiconductor wafers 100 are accomplished by a wafer transferarm/tray 91B which is connected to and driven by a rotational drive unit91A. This transfer chamber 91 is so shielded like the treating chambers90 and 92 to 93 from the atmosphere of the outside of the apparatus thatit is held under a high vacuum having no H₂ O or O₂.

The transfer chamber 91 is equipped with an ultraviolet ray irradiationlamp 95, as shown in FIGS. 62 and 63. This ultraviolet ray irradiationlamp 95 is constructed to irradiate the surface of the semiconductorwafers 100 conveyed to the transfer chamber 91 with an ultraviolet rayhaving an energy of at least about 5 to 6 eV! thereby to break thecoupling between the Si and the F, as will be described hereinafter.

The aforementioned pretreating chamber 92 is equipped with a pretreatingmodule 92A. This pretreating module 92A is composed mainly of a hotplate 92a, a temperature controller 92b, an exhaust pipe 92c, a vacuumpump 92d, a radical generator tube 92e, a microwave generator unit 92f,a microwave power source 92g and a gas control unit 92h. In short, thepretreating chamber 92 is enabled to anisotropically etch off thenatural silicon oxide film which is formed on the surface of thepolycrystalline silicon film over the surface of the semiconductorwafers 100. This polycrystalline silicon film corresponds to the lowerelectrode layer 35 of the information storing capacity element C of thestacked structure in the DRAM 1 of the aforementioned embodiment I. Theanisotropic (or dry) etching uses oxygen gases and a halogen compound(e.g., CHF₃ or CF₄).

The first reactor chamber 93 and the second reactor chamber 94 areindividually equipped with the common (or independent) cleaning modules93A. Each of the first reactor chamber 93 and the second reactor chamber94 is composed, as shown in FIG. 64 (presenting an essential portionschematically), mainly of a source gas supply tube 93a, a source gasblow-off plate 93b, plate cooling pipes 93c, a succeptor 93d, a waferheating heater 93e, reaction chamber cooling pipes 93f, a exhaust pipe93g a vacuum gate valve 93h and a vacuum pump 93i. Although notlimitative thereto, the first reactor chamber 93 is enabled to depositthe silicon nitride film (i.e., the lower silicon nitride film 36A ofthe dielectric film 36), and the second reactor chamber 94 is enabled todeposit the polycrystalline silicon film (i.e., the lower electrodelayer 35 or the upper electrode layer 37).

If the DRAM 1 is constructed to have a high capacity of 16 Mbits3, it isrequired of a high controllability of the thickness of the lowerelectrode layer 35 or the dielectric film 36 of the information storingcapacity element C of the stacked structure, for example. Therefore, theleaf type CVD apparatus is suited for the fabrication of the DRAM 1.Each of the first reactor chamber 93 and the second reactor chamber 94is arranged with the source gas blow-off plate 93b in a position facingthe surface, on which the semiconductor wafer 100 held on the succeptor93d is to be deposited, so that it can deposit a film of homogeneousthickness and quality on the surface of the semiconductor wafer 100.Each of the first reactor chamber 93 and the second reactor chamber 94is held as a whole at a low temperature so that only the semiconductorwafer 100 is heated to a temperature optimum for the reaction by thewafer heating heater 93e.

On the other hand, the aforementioned source gas blow-off plate 93b isequipped with the plate cooling pipes 93c so as to drop the temperaturerise of the semiconductor wafers 100 due to the radiation heat. Sincethe fine particles generated instantly by the reaction in the vicinityof the blow-off port of the source gases will grow to large particles orforeign substance at an instant when they reach the surface of thesemiconductor wafer 100, the source gas blow-off plate 93b has to becooled by the plate cooling pipes 93c.

The aforementioned leaf type CVD apparatus is constructed to accomplisha series of continuous treatments, for which the pretreating chamber 92is disposed upstream of each of the first reactor chamber 93 and thesecond reactor chamber 94, as will be described in the following.

First of all, as shown in FIG. 62, the semiconductor wafer 100 istransferred from the load/unload chamber 90 through the transfer chamber91 to the pretreating chamber 92. The polycrystalline silicon film isdeposited on the surface of the semiconductor wafer 100.

Next, as shown in FIGS. 62 and 63, the pretreating chamber 92anisotropically etches off the natural silicon oxide film which isformed on the surface of the polycrystalline silicon film of thesemiconductor wafer 100. This anisotropic etching is accomplished byusing the oxide gases and the halogen compound as the etching gases.

Next, the semiconductor wafer 100 having its natural silicon oxide filmremoved by the pretreating chamber 92 is transferred to the transferchamber 91, in which the surface of the aforementioned polycrystallinesilicon film is exposed to the ultraviolet ray by the ultraviolet rayirradiation lamp 95. This irradiation of the ultraviolet ray releasedthe fluorine (F), which is produced by the anisotropic etching on thesurface of the aforementioned polycrystalline silicon film, as theradicals from the surface of the polycrystalline silicon film.

Next, the semiconductor wafer 100 is transferred through the transferchamber 91 sequentially to the first reactor chamber 93 and the secondreactor chamber 94, in which the silicon nitride film or the like isdeposited on the surface of the polycrystalline silicon film.

Then, the semiconductor wafer 100 thus treated is accommodated throughthe transfer chamber 91 by the load/unload chamber 90.

Thus, a film depositing method of depositing the insulating film or theconducting film on the polycrystalline silicon film (or the surface ofthe semiconductor wafer 100) deposited on the surface of thesemiconductor wafer 100, comprises: the step of exposing the surface ofthe polycrystalline film of the surface of the semiconductor wafer 100by cleaning the surface of said polycrystalline silicon film in thevacuum system in the pretreating chamber 92; and the step of depositingthe insulating film or the conducting film on the surface of saidpolycrystalline silicon film in the same vacuum system as that of saidcleaning step in said first reactor chamber 93 or said second reactorchamber 94. Thanks to this construction, after the natural silicon oxidefilm film formed on the surface of the aforementioned polycrystallinesilicon film has been cleaned off, the insulating film or the conductingfilm can be deposited on the surface of the aforementionedpolycrystalline silicon film without contact with the atmosphere so thatthe natural silicon oxide film need not be sandwiched between thesurface of the aforementioned polycrystalline silicon film and theaforementioned insulating film or conducting film. As a result, thethicknesses of the surface of the aforementioned polycrystalline siliconfilm and the insulating film to be deposited on the former surface suchas the silicon nitride film 36A of the dielectric film 36 can be reducedto an extent corresponding to the aforementioned natural silicon oxidefilm so that the amount of charge storage of the information storingcapacity element C of the stacked structure can be increased. Moreover,the conduction between the surface of the polycrystalline silicon filmand the conducting film to be deposited on the former surface can beensured.

On the other hand, a film depositing film of depositing the insulatingfilm on the surface of the polycrystalline silicon film (or thesemiconductor wafer 100) overlying the semiconductor wafer 100comprises: the step of exposing the surface of the polycrystallinesilicon film overlying the aforementioned semiconductor wafer 100 to theoutside by cleaning the surface of said polycrystalline silicon film inthe vacuum system by the anisotropic etching using the halogen compound;the step of exposing the surface of the polycrystalline silicon film tothe outside; the step of irradiating the exposed surface of thepolycrystalline silicon film with the ultraviolet ray in the same vacuumsystem as that of said cleaning step; and the step of depositing theaforementioned insulating film (e.g., the silicon nitride film) on thesurface of the aforementioned polycrystalline silicon film in the samevacuum system as that of said cleaning step. Thanks to thisconstruction, the radicals of the halogen element sticking to thesurface of the aforementioned polycrystalline silicon film, when saidsurface is cleaned, can be removed by the aforementioned ultravioletray. As result, it is possible to reduce the augmentation of the leakagecurrent and the changes of the etching rate of the insulating filmdeposited on the surface of the aforementioned polycrystalline siliconfilm, such as the silicon nitride film.

(Embodiment V)

The present embodiment V is directed to a fifth embodiment of thepresent invention, in which the suitable process for forming the lowerelectrode layer 35 and the apparatus for executing the process have beendescribed in the information storing capacity element C of the stackedstructure of the memory cell M of the DRAM 1 of the foregoing embodimentI.

The leaf type CVD method according to the embodiment V of the presentinvention is shown in FIG. 65 (presenting a time chart showing thecontrolling operations of the source gas valves of the CVD apparatus)and FIG. 66 (presenting a timing chart showing the flow rate of theaforementioned source gases.

The lower electrode layer 35 of the information storing capacity elementC of the stacked structure of the memory cell M of the DRAM 1 of theforegoing embodiment I of the foregoing embodiment I is thickened toincrease the amount of charge storage, as has been describedhereinbefore. In case the lower electrode layer 35 is thick, it isdifficult to introduce the n-type impurity for reducing the resistance.In the present embodiment V, the so-called "doped polysilicontechnology", i.e., the technology for depositing the polycrystallinesilicon film doped with the aforementioned n-type impurity is used toform the aforementioned lower electrode layer 35.

The polycrystalline silicon film to be deposited by the CVD method butnot doped with the n-type impurity usually has a high step coverage atthe underlying stepped portion, but it is difficult to introduce then-type impurity after the deposition if the thickness is enlarged. Onthe contrary, the polycrystalline silicon film to be deposited by theCVD method and doped with the n-type impurity is easy to introduce then-type impurity but has an inferior step coverage at the underlyingstepped portion. In the present embodiment V, therefore, thepolycrystalline silicon film underpaid with the n-type impurity and thepolycrystalline silicon film doped with the n-type impurity arealternately laminated to improve the step coverage at the underlyingstepped portion. After the individual polycrystalline silicon films havebeen deposited, they are subjected to the heat treatment to introducethe n-type impurity from the polycrystalline silicon film doped with then-type impurity to the polycrystalline silicon film underpaid with then-type impurity.

FIG. 65 presents the opening and closing operations of the controlvalues which are arranged at the source gas supply pipes of the CVDapparatus. The source gases used are inorganic silane (e.g., SiH₄ or Si₂H₆) gases and phosphine (i.e., PH₃) gases. The valve for controlling thesupply of the inorganic silane gases of the source gases is opened forsuch a constant time as to achieve a predetermined film thickness, asshown in FIG. 65(A). On the contrary, the control valve for supplyingthe phosphine gases periodically repeats its opening and closingoperations, as shown in FIG. 65(B), while the inorganic silane gascontrol valve is open. FIG. 66(A) indicates the flow rate of theinorganic silane gases, the supply of which is controlled by theaforementioned control valve, and FIG. 66(B) indicates the flow rate ofthe phosphine gases. Moreover, the interrupted supply of the phosphinegases can also be controlled by varying the set value of the mass flowcontroller. The switching of the interrupted supply of the phosphinegases by the control valve or the mass flow controller can beaccomplished at a speed as high as about 1 to 2 sec.!.

As shown in FIG. 67 (presenting the leaf type CVD apparatusschematically), on the other hand, stop valves 93j may be disposed inthe vicinity of the reaction chamber 93 (or 94) of the source gas (PH₃)supply tube 93a so that they may supply the source gases to the reactionchamber 83 and the vacuum pump 93i individually at high rates. The CVDapparatus, as shown in FIG. 67, can interchange the interrupted supplyof the phosphine gases at an interval of about 0.1 sec.!.

Thus, a film depositing process for depositing the polycrystallinesilicon film (e.g., the lower electrode layer 35) on the underlyingsurface having the stepped shape, comprising: the step of alternatelydepositing pluralities of polycrystalline silicon films containing then-type impurity for reducing the resistance and polycrystalline siliconfilm containing none of said n-type impurity over said underlyingsurface; and the step of diffusing said n-type impurity from thepolycrystalline silicon film containing said n-type impurity to thepolycrystalline silicon film containing none of said n-type impurity byheat-treating the polycrystalline silicon films thus laminated. Thanksto this construction, in the regions of the stepped shape of theaforementioned underlying surface so that the thicknesses of thepolycrystalline silicon films can be uniformed. At the same time, theaforementioned n-type impurity can be diffused from the polycrystallinesilicon films containing the n-type impurity to the polycrystallinesilicon films containing none of the n-type impurity so that thepolycrystalline silicon films thus laminated can retaining a largethickness while having their impurity concentrations uniformed.

In a film depositing method of depositing the polycrystalline siliconfilms on the underlying surface having the stepped shape, on the otherhand, the inorganic silane gases are supplied at the constant flow rateto the inside of the vacuum system for depositing the polycrystallinesilicon films to deposit the polycrystalline silicon films containing noimpurity on the basis of the thermal decomposition, and the phosphinegases are supplied at the periodically varying flow rate to the insideof the vacuum system so that the polycrystalline silicon films depositedmay contain the n-type impurity (e.g., P) periodically. Thanks to thisconstruction, the polycrystalline silicon films containing theaforementioned n-type impurity and the polycrystalline silicon filmscontaining none of the n-type impurity can be individually andcontinuously in the common vacuum system so that the deposition time ofthe polycrystalline silicon films can be shortened. In short, thethroughput of the DRAM 1 can be improved.

(Embodiment VI)

In the process for fabricating the aforementioned DRAM 1, the presentembodiment VI is directed to a fixth embodiment of the presentinvention, in which the number of steps of setting the threshold voltageof the MISFETs is reduced.

The process for fabricating the DRAM 1 according to the embodiment VI ofthe present invention will be briefly described with reference to FIGS.68 to 71 (presenting an essential portion in section at the individualfabrication steps).

In the present embodiment VI, the threshold voltages of the six MISFETsused in the DRAM 1 of the foregoing embodiment I are set. Specifically,the n-channel MISFETs are exemplified by the memory cell selectingMISFETs Qs of the memory cells M, the n-channel MISFETs Qn having thestandard threshold voltage, and the n-channel MISFETs Qn having a lowthreshold voltage. The p-channel MISFETs are exemplified by thep-channel MISFETs Qp having the standard threshold voltage, thep-channel MISFETs Qp having a low threshold voltage, and the p-channelMISFETs Qp having a high threshold voltage.

The aforementioned memory cell selecting MISFETs Qs (to be formed in aregion in the later-described fabrication process) have their thresholdvoltage set at the highest level of the n-channel MISFETs. Specifically,the memory cell selecting MISFETs Qs have their surface impurityconcentrations increased to have their threshold voltage set at the highlevel, because the p-type semiconductor regions 25B are formed over theprincipal surface portions of the p⁻ -type well region 22 in the memorycell array 11E. More specifically, the memory cell selecting MISFETs Qshave their threshold voltages set at 0.8 V! in case they are formed tohave a gate length of 0.8 μm!.

The n-channel MISFETs Qn (to be formed in regions III) having theaforementioned standard threshold voltage are used in most of theperipheral circuits excepting the sense amplifiers (SA) 13, namely, inthe regions to be operated at the low power source voltage Vcc. Then-channel MISFETs Qn having the standard threshold voltage have theirthreshold voltage set at 0.5 V! in case they are formed to have a gatelength of 0.8 μm!.

The n-channel MISFETs Qn (to be formed in regions II) having theaforementioned low threshold voltage are used mainly in theaforementioned sense amplifier circuits 13 and the output buffercircuits 1702. These n-channel MISFETs Qn having the low thresholdvoltage are constructed to have a large gate length so as to reduce thefluctuations of the threshold voltage based on the treating dispersionsof the gate electrodes 27, especially on the fluctuations of the gatelength. Since the sense amplifier circuits 13 have their informationdecision sensitivity dropped for the large gate length, the thresholdvoltage of the n-channel MISFETs Qn is set at the low level. Since,moreover, the output buffer circuits 1702 have their downstream unitdrivability dropped for the large gate length, the n-channel MISFETs Qnhave their threshold voltage set at the low level. The n-channel MISFETsQn having this low threshold voltage are formed to have a gate length of1.4 μm! to set the threshold voltage set at 0.5 V!. In other words, then-channel MISFETs Qn having the low threshold voltage is set to have athreshold voltage of 0.3 V! if the gate length is converted to 0.8 μm!.

On the other hand, the p-channel MISFETs Qp (to be formed in regions IV)having the aforementioned standard threshold voltage are used in mostportions of the peripheral circuits excepting the sense amplifiercircuits 13, namely, in the regions to be operated at the low powersource voltage Vcc. The p-channel MISFETs Qp having this standardthreshold voltage are set to have a threshold voltage of -0.5 V! in casethey are formed to have a gate length of 0.8 μm!.

The p-channel MISFETs Qp (to be formed in regions V) having theaforementioned low threshold voltage are used in the aforementionedsense amplifier circuits 13. Moreover, the p-channel MISFETs Qp havingthe low threshold voltage are used as one of the p-channel MISFETs Qpfor establishing the reference potential (e.g., the reference potentialof -1.0 V! for generating the aforementioned low power source voltageVcc of about 3.3 V!) of the VCC limiter circuits 1804 and the VDLlimiter circuits 1810. The p-channel MISFETs Qp having the low thresholdvoltage used as the sense amplifier circuits 13 are formed to have agate length of 1.4 μm! and a threshold voltage of -0.5 V! (which is lowin its absolute value). In other words, the p-channel-MISFETs Qp havingthe low threshold voltage are set to have a threshold voltage of -0.2 V!if the gate length is converted to 0.8 μm!. On the other hand, thep-channel MISFETs Qp having the low threshold voltage used in thereference voltage generator circuits are formed to have a gate length of8 μm! and a threshold voltage of -0.6 V!. In other words, the p-channelMISFETs Qp having the low threshold voltage are set to have a thresholdvoltage of -0.2 V! if the gate length is converted to 0.8 μm!.

The p-channel MISFETs Qp (to be formed in regions VI) having theaforementioned high threshold voltage are used as the other p-channelMISFETs Qp for establishing the reference potential of theaforementioned reference voltage generator circuits. The p-channelMISFETs Qp having the high threshold voltage to be used in the referencevoltage generator circuits are set to have a gate length of 8 μm! and athreshold voltage of -1.6 V! (which is high in its absolute value). Inother words, the p-channel MISFETs Qp having the high threshold voltageis set to have a threshold voltage of -1.2 V! if the gate length isconverted to 0.8 μm!.

Next, the process for forming the individual MISFETs of this DRAM 1 willbe brief described in the following.

First of all, like the process for fabricating the DRAM 1 of theforegoing embodiment I, the principal surface portions of the p⁻ -typesemiconductor substrate 20 are formed sequentially with the n⁺ -typewell regions 21 and the p⁻ -type well regions 22 and then with theinterlayer separating insulating film 23, the p-type channel stopperregions 25A and the p-type semiconductor regions 25B. The state thusformed is shown in FIG. 68. Since the gap between the p-channel MISFETsQp is reduced to drop the separating ability as a result of the highintegration of the aforementioned DRAM 1, the n⁺ -type well regions 21have their impurity concentration set at a slightly high value.Specifically, the n⁺ -type well regions 21 are set to have an impurityconcentration of about 1×10¹³ to 3×10¹³ atoms/cm² !, for example. Thisimpurity concentration of the n⁺ -type well regions 21 can set the highthreshold voltage (in its absolute value) of the p-channel MISFETs Qp tobe formed in the regions VI. Since, on the other hand, the gate lengthof the n-channel MISFETs Qn having the standard threshold voltage isreduced as a result of the high integration of the DRAM 1, the substrateeffect constant is dropped so that the impurity concentration of the p⁺-type well regions 22 can be set at a slightly high value so as tosuppress the short channel effect. Specifically, the p⁻ -type wellregions 22 is set to have an impurity concentration of about 7×10¹² to9×10¹² atoms/cm² !, for example. This impurity concentration of the p⁻-type well regions 22 can set the low threshold voltage of the n-channelMISFETs Qn to be formed in the regions II. The high threshold voltage ofthe memory cell selecting MISFETs Qs of the regions I can be set as aresult of the gush of the impurity from the p⁻ -type well regions 22 andthe p-type semiconductor regions 25B.

Next, as shown in FIG. 69, the p-type impurity 22p is introduced intothe regions III to set the standard threshold voltage of the n-channelMISFETs Qn. This p-type impurity 22p used is the B having an impurityconcentration of about 1×10¹² to 2×10¹² atoms/cm² !, for example, and isintroduced by the ion implantation having an energy of about 15 to 25KeV!. Upon the introduction of the p-type impurity 22p, there is used animpurity introduction mask (of a photoresist film, for example) 110, asshown in FIG. 69. Next, as shown in FIG. 70, the standard voltage of thep-channel MISFETs Qp is set by introducing a p-type impurity 21p₁ intothe regions IV. This p-type impurity 21p₁ used is the B having animpurity concentration of about 2.0×10¹² to 2.2×10¹² atoms/cm² !, forexample, and is introduced by the ion implantation of about 15 to 25KeV!. Upon the introduction of the p-type impurity 21p₁, there is usedan impurity introduction mask (of a photoresist film, for example) 111,as shown in FIG. 70.

Next, as shown in FIG. 71, a p-type impurity 21p₂ is introduced into theregions V to set the low threshold voltage of the p-channel MISFETs Qp.This p-type impurity 21p₂ used is the B having an impurity concentrationof about 2.4×10¹² to 2.6×10¹² atoms/cm² !, for example, and isintroduced by the ion implantation having an energy of about 15 to 25KeV!. Upon the introduction of this p-type impurity 21P₂, there is usedan impurity introduction mask (of a photoresist film) 112, as shown inFIG. 70.

Incidentally, the introduction order of the aforementioned thresholdvoltage adjusting impurities should not be limited to theabove-specified one, but either of the impurities may be introducedearlier or later.

Thus, in the DRAM 1 having the complementary MISFETs, the processcomprises: the step of forming at the principal portions of thedifferent regions of the p⁻ -type semiconductor substrate 20 with the p⁻-type well regions 22 at the impurity concentration for setting the lowthreshold voltage of the n-channel MISFETs Qn and the n⁻ -type wellregions 21 at the impurity concentration for setting the high thresholdvoltage (in its absolute value of the p-channel MISFETs Qp; and the stepof setting the standard threshold voltage of the n-channel MISFETs Qn byintroducing the threshold voltage adjusting p-type impurity 22p into theprincipal surface portions of the p⁻ -type well regions 22 and settingthe standard (or low in its absolute value) threshold voltage of thep-channel MISFETs by introducing the threshold voltage adjustingimpurity 21p₁, (or 21p₂) into the principal surface portions of the n⁻-type well regions 21. Thanks to this construction, the low thresholdvoltage of the n-channel MISFETs Qn can be set by the impurityconcentration of the p⁻ -type well regions 22, and the high thresholdvoltage of the p-channel MISFETs Qp can be set by the impurityconcentration of the n⁻ -type well regions 21. Thus, the four kinds ofthreshold voltages can be set by the individually twice introductions ofthe threshold voltage adjusting p-type impurities 22p and 21p₁ (or 21p₂)so that the number of the introduction steps of the threshold voltageadjusting impurities can be reduced.

Moreover, the n⁻ -type well regions 21 and the p⁻ -type well regions 22are individually formed in selfalignment with the principal surfaceportions of the p⁻ -type semiconductor substrate 20. Thanks to thisconstruction, the step of exposing the surface of the p⁻ -typesemiconductor substrate 20 other than the n⁻ -type well regions 21 andp⁻ -type well regions 22 is eliminated so that the number of thefabrication steps of the DRAM 1 can be reduced to an extentcorresponding to the eliminated step.

Moreover, in the DRAM 1 including the p-channel MISFETs Qp forgenerating the reference voltage and the p-channel MISFETs Qp forgenerating the standard reference voltage, the process comprises: thestep of forming the n⁻ -type well regions 21 at an impurityconcentration for setting the high (in its absolute value) thresholdvoltage of the p-channel MISFETs Qp for generating the referencevoltage; the step of setting the standard threshold voltage (or the lowthreshold voltage) of the p-channel MISFETs Qp by introducing thethreshold voltage adjusting impurity 21p₁ (or 21p₂) into the differentregions of the n⁻ -type well regions 21; and the step of setting the lowthreshold voltage (or the standard threshold voltage) of the p-channelMISFETs Qp by introducing the threshold adjusting impurity 21p₂ (or21p₁) into the different regions of the n⁻ -type well regions 21. Thanksto this construction, the low threshold voltage of the p-channel MISFETsQp for generating the reference voltage can be set by the impurityconcentration of the n⁻ -type well regions 21 so that the three kinds ofthreshold voltages can be set by the individual twice threshold voltageadjusting impurities 21p₁ and 21p₂. As a result, it is possible toreduce the number of steps of introducing the threshold voltageadjusting impurities.

(Embodiment VII)

In the DRAM 1 of the foregoing embodiment I, the present embodiment VIIis directed to a seventh embodiment of the present invention, in whichthe amount of charge storage of the information storing capacityelements C of the stacked structure of the memory cells M is increased.

An essential portion of the DRAM 1 according to the embodiment VII ofthe present invention is shown in FIG. 72 (presenting an essentialportion of the memory cell array at a predetermined fabrication step insection).

As shown in FIG. 72, the memory cell M of the DRAM 1 of the presentembodiment VII is formed with grooves 35g in the lower electrode layer35 of the information storing capacity element C of the stackedstructure. Specifically, the information storing capacity element C ofthe stacked structure is enabled to increase the surface in the verticaldirection by the inner walls of the grooves 35g of the lower electrodelayer 35 so that it can improve the charge storage. Those grooves 35gare formed to cross the lower electrode layer 35 in the direction ofextending the word lines (WL) 27.

Next, the process for forming the information storing capacity element Cof the stacked structure of the aforementioned memory cell M will bebriefly described with reference to FIGS. 73 to 76 (presenting anessential portion at the individual fabrication steps in section).

First of all, like the process of fabricating the DRAM 1 of theforegoing embodiment 1, the memory cell selecting MISFETs Qs of thememory cells M are formed, and the interlayer insulating film 33 is thenformed, as shown in FIG. 73.

Next, as shown in FIG. 74, a polycrystalline silicon film 35B is formedover all the surface of the substrate including the surface of theinterlayer insulating film 33. The polycrystalline silicon film 35B isformed to have a large thickness, as has been described hereinbefore,and is doped with an n-type impurity for reducing the resistance. Thisn-type impurity is introduced, according to the method described inconnection with the foregoing embodiment I, by depositing the dividedplural layers of the polycrystalline silicon film and by introducing then-type impurity for each of the depositions by the hot diffusion method.On the other hand, the n-type impurity is also introduced, according tothe method described in connection with the foregoing embodiment V, byalternately laminating the polycrystalline silicon film doped with noneof the n-type impurity and the polycrystalline silicon film doped withthe n-type impurity and by the subsequent heat treatment.

Next, as shown in FIG. 75, at the connected portions between the memorycell selecting MISFETs Qs and the lower electrode layer 35 of theinformation storing capacity elements C of the stacked structure, thepolycrystalline silicon film 35B and the interlayer insulating film 33are individually and sequentially removed to form the grooves 35g. Thesegrooves are formed by the anisotropic etching, for example. When thesegrooves 35g are formed, the surfaces of the other n-type semiconductorregions 29 of the memory cell selecting MISFETs Qs are exposed to theoutside.

Next, all the surfaces of the polycrystalline silicon film 35B includingthe surfaces of the inner walls of the aforementioned grooves 35g andthe surface of the exposed n-type semiconductor regions 29 are formedthereover with a polycrystalline silicon film 35C. This polycrystallinesilicon film 35C is formed to have such a small thickness as not to burythe insides of the aforementioned grooves 35g (i.e,. to retain thestepped shape). The polycrystalline silicon film 35C is doped with ann-type impurity, this n-type impurity is introduced at such a lowerimpurity concentration than that of the polycrystalline silicon film 35Bas to reduce the short channel effect of the memory cell selectingMISFETs Qs.

Next, as shown in FIG. 76, the aforementioned polycrystalline siliconfilms 35C and 35B are individually and sequentially patterned to formthe lower-electrode layer 35. The subsequent fabrication process issubstantially similar to that of the DRAM 1 of the foregoing embodimentI, and its description will be omitted here.

Thus, in the information capacity storing elements C of the memory cellsM of the DRAM 1, the amount of the charge storage can be improved to anextent corresponding to the aforementioned grooves 35g by forming thegrooves 35g in the lower electrode layer 35.

On the other hand, the lower electrode layer 35 of the informationstoring capacity elements C of the stacked structure may be formed withthe grooves 35g across the extending direction of the complementary datalines (DL) 50, as shown in FIG. 77 (presenting the essential portion ofthe memory cell at a predetermined fabrication step in section). Sincethe DRAM 1 of the present embodiment VII adopts the folded bit linemethod, the arrangement gap of the lower electrode layer 35 in theextending direction of the word lines 27 is so small that the lowerelectrode layer 35 is formed in the rectangular shape which is elongatedin the extending direction of the complementary data lines 50. As aresult, the increase in the surface area of the lower electrode layer 35due to the aforementioned grooves 35g is far larger than those of theaforementioned ones.

The process of forming the information storing capacity elements C ofthe stacked structure, as shown in FIG. 77, will be briefly describedwith reference to FIGS. 78 to 80 (presenting essential portions at theindividual fabrication steps in section).

First of all, as shown in FIG. 78, the whole surface of the substrateincluding the surface of the interlayer insulating film 33 is formedthereover with the polycrystalline silicon film 35B.

Next, as shown in FIG. 79, the grooves 35g are formed in thepolycrystalline silicon film 35B.

Next, the polycrystalline silicon film 35C is formed over theaforementioned polycrystalline silicon film 35B, and thesepolycrystalline silicon films 35C and 35B can be individually patternedto form the lower electrode layer 35, as shown in FIG. 80.

Moreover, the lower electrode layer 35 of the information storingcapacity elements C of the stacked structure, as has been described withreference to FIGS. 72 to 76, can improve the amount of charge storage,as shown in FIGS. 81 to 84 (presenting essential portions at theindividual fabrication steps in section).

First of all, as shown in FIG. 81, the polycrystalline silicon film 35Bis formed, and the grooves 35g are then formed, as shown in FIG. 82.

Next, as shown in FIG. 83, the polycrystalline silicon film 35B ispatterned in advance in the shape of the lower electrode layer 35, andthe grooves 35g are formed.

Next, the whole surface of the substrate including the surfaces of theinner walls of the aforementioned grooves 35g, the surface of thepolycrystalline silicon film 35B and the exposed surface of the n-typesemiconductor region 29 is formed with the polycrystalline silicon film35C.

Next, this polycrystalline silicon film 35C is patterned by theanisotropic etching to form the lower electrode layer 35. This lowerelectrode layer 35 is enabled to improve the amount of charge storagelike before by the aforementioned grooves 35g and to leave thepolycrystalline silicon film 35C on the outer circumference side wallsof the polycrystalline silicon film 35B of the lower electrode layer 35.As a result, it is possible to improve the amount of charge storage toan extent corresponding to the thickness of the polycrystalline siliconfilm 35C thus left.

Moreover, the lower electrode layer 35 of the information storingcapacity elements C of the stacked structure, which has been describedwith reference to FIGS. 77 to 80, can also improve the amount of chargestorage, as shown in FIGS. 85 to 88 (presenting essential portions atthe individual fabrication steps in section).

First of all, the polycrystalline silicon film 35B is formed, as shownin FIG. 85, and the grooves 35g are then formed, as shown in FIG. 86.

Next, as shown in FIG. 87, the polycrystalline silicon film 35B ispatterned in advance in the shape of the lower electrode layer 35.

Next, the whole surface of the substrate including the surfaces of theinner walls of the aforementioned grooves 35g, the surface of thepolycrystalline silicon film 35B and the exposed surface of the n-typesemiconductor region 29 is formed thereover with the polycrystallinesilicon film 35C.

Next, this polycrystalline silicon film 35C is patterned by theanisotropic etching to form the lower electrode layer 35. Since thislower electrode layer 35 can leave the polycrystalline silicon film 35Con the outer circumference side walls of the polycrystalline siliconfilm 35B, it can improve the amount of electric charge further to anextent corresponding to the thickness of the polycrystalline siliconfilm 35C thus left.

(Embodiment VIII)

In the fabrication method of the DRAM 1 of the foregoing embodiment I,the present embodiment VIII is directed to an eighth embodiment of thepresent invention, in which the degree of integration is improved byreducing the mask registration (or alignment) displacement.

In the fabrication process of the DRAM 1 of the embodiment VIII of thepresent invention has its alignment relations shown in FIG. 89(presenting an alignment tree).

The DRAM 1 of the foregoing embodiment I has its upper layer patternaligned (or registered) with its lower layer pattern at the fabricationstep. FIG. 89(A) shows the relations of the alignment in the X direction(e.g., in the extending direction of the word lines). The DRAM 1 of thepresent embodiment VIII has its alignment referred to the n⁻ -type wellregions 21. The element separating insulating films 23 have theirX-direction aligned to the n⁻ -type well regions 21. The gate electrodes27 (or the word lines) 27 have their X direction aligned to the elementseparating insulating films 23. The gate electrodes 27 provide thereference for the alignment of their upper layer. The lower electrodelayer 35, the upper electrode layer 37 and the connecting holes 40 ofthe information storing capacity elements C of the stacked structureindividually have their X direction aligned to the aforementioned gateelectrodes 27.

On the contrary, FIG. 89(B) shows the relations of the alignment in theY direction (i.e., in the extending direction of the complementary datalines). The DRAM 1 of the present embodiment VIII is aligned in the twoX and Y directions. Likewise, the n⁻ -type well regions 21 provide thereference for the alignment, and the element separating insulating films23 align the n⁻ -type well regions 21 in the Y direction. The gateelectrodes 27 align the element separating insulating films 23 in the Ydirection. Unlike the alignment in the X direction, the lower electrodelayer 35 aligns the element separating insulating films 23 in the Ydirection. The upper electrode layer 37 and the connecting holes 40Aindividually align the aforementioned gate electrodes 27 in the Ydirection.

In case the lower electrode layer 35 of the information storing capacityelements C of the stacked structure are seriously misaligned from theaforementioned element separating insulating films 23, the connectingholes 34 for connecting the other n-type semiconductor regions 29 of thememory cell selecting MISFETs Qs and the lower electrode layer 35 areopened (as shown in FIG. 1). This opening causes the surfaces of then-type semiconductor regions 29 exposed from the connecting holes 34,when the lower electrode layer 35 is treated, to be etched. As a result,the misalignment of the lower electrode layer 35 from the elementseparating insulating films 23 has to be minimized.

In case the aforementioned lower electrode layer 35 is aligned simply inthe X and Y directions with respect to the gate electrodes 27, there areestablished misalignments σ between the element separating insulatingfilms 23 and the gate electrodes 27 and between the gate electrodes 27and the lower electrode layer 35, so that that the misalignment of thelower electrode layer 35 to the element separating insulating films 23is 1.4 σ.

In the present embodiment VIII, therefore, the lower electrode layer 35is aligned in the X direction (or in the Y direction) with respect tothe gate electrodes 27, i.e., the pattern underlying the former just byone layer, as shown in FIG. 89(A), and in the Y direction (or in the Xdirection) with respect to the element separating insulating films 23,i.e., the pattern underlying the former by two layers, as shown in FIG.89(B). In other words, the lower electrode layer 35 of the informationstoring capacity elements C of the stacked structure is misaligned onlyby the value σ from the element separating insulating films 23 or thegate electrodes 27. Since the lower electrode layer 35 provides noreference for the alignment, it can be aligned across the aforementioneddifferent layers.

Thus, in an alignment method of aligning the patterns of the threedifferent layers of the element separating insulating films 23, the gateelectrodes 27 and the lower electrode layer 35 in the X direction andthe Y direction, the gate electrodes (i.e., the second layer pattern) 27are aligned in the X direction and the Y direction with respect to theunderlying element separating insulating films (i.e., the first layerpattern) 23, the lower electrode layer (i.e., the third layer pattern)35 to be formed over the gate electrodes 27 is aligned in the Xdirection (or in the Y direction) with respect to the underlying gateelectrode 27 and in the Y direction (or in the X direction) with respectto the underlying element separating insulating films 23. Thanks to thisconstruction, it is possible to substantially equalize the misalignmentbetween the element separating insulating films 23 and the gateelectrodes 27 and the misalignment between the element separatinginsulating films 23 and the lower electrode layer 35 so that themisalignment Between the element separating insulating films 23 and thelower electrode layer 35 can be reduced. As a result, the degree ofintegration of the DRAM 1 can be improved to an extent corresponding tothe masking allowance at the fabrication step. As has been describedhereinbefore, moreover, the connecting holes 34 for connecting the othern-type semiconductor regions 29 of the memory cell selecting MISFETs Qsand the lower electrode layer 35 are not excessively opened.

(Embodiment IX)

In the DRAM 1 of the foregoing embodiment I, the present embodiment IXis directed to a ninth embodiment of the present invention fordescribing a suitable process for forming a target mark when thealignment method described in the foregoing embodiment VIII is executed.

The structure of the target mark portion of the DRAM 1 according to thepresent embodiment IX is shown in FIG. 90 (presenting an essentialportion in section).

As shown in FIG. 90, a target mask TM is defined by the connecting holes53D, which are formed in the interlayer insulating film 53 of the DRAM1, and the wiring lines 55 which are formed over the interlayerinsulating firm 53. The target mark M is arranged in the semiconductorwafer in the scribe area between the regions for forming the DRAM 1, theinside of the regions for forming the DRAM 1, and the regions forforming the dummy DRAM 1 (which is not used as the DRAM but as thetarget mark for alignment).

The target mark TM thus formed is formed by forming the connecting holes53D in the regions in which the wiring lines (of a transition-metalfilm) 52 are not over the interlayer insulating film 51). Since none ofthe wiring lines 52 is present below, the transition-metal film 54 to beburied by the selective CVD method is not deposited in the connectingholes 53D. Since the wiring lines 55 used are made of the aluminum alloyfilm 55B having an inferior step coverage, the stepped shape is formedon the surface of the wiring lines 55 by the stepped shape of theconnecting holes 53D. This stepped shape is used as the aforementionedtarget mark TM.

Thus, the target mark TM can be formed at the step shared with the stepof forming the connecting holes 53D of the fabrication step of the DRAM1 and the step of formign the wiring lines 55 so that the number of thefabrication steps can be reduced.

(Embodiment X)

In the process of fabricating the DRAM 1 of the foregoing embodiment I,the present embodiment X is directed to a tenth embodiment of thepresent invention, in which the focal depth and resolution of theexposure of the photolithography technology are improved.

The individual steps of the photolithography used in the fabricationprocess of the DRAM 1 according to the embodiment X of the presentinvention are shown in FIG. 91 (presenting a conceptional diagram) andFIG. 2 (presenting a step flow chart).

The photolithography technology of the present embodiment X uses theFLEX (Focus Latitude Enhancement EXposure) method and the CEL (ContrastEnhancement Lithography) method to improve the focal depth and theresolution for the exposure of the photo resist film. The exposingprocedures of the photolithography technology are as follows:

First of all, as shown in FIGS. 91 and 92, a photoresist film 120 isapplied <1> to the semiconductor wafer 100.

Next, a photochromic CEL material 121A is dropped to the surface of thephotoresist film 120 applied to the aforementioned semiconductor wafer,thereby to apply <2> a photochromic CEL film 121. The photochromic CELfilm 121 used is nitron, for example, as shown in FIG. 93 (presentingthe structural formula). This photochromic CEL film 121 has a propertyto become transparent (or bleached) if it is irradiated (as started attl) with a predetermined amount or more of light, as shown in FIG. 94(presenting the transmittance to the exposure). Moreover, thephotochromic CEL film 121 does not have a property to become opaque whenthe optical irradiation is stopped (as ended at t₂). Still moreover,these properties are contrary to each other.

Next, in the projecting exposure device, the pattern of reticle 125 istransferred <3> to the photoresist film 120, which is applied to thesurface of the aforementioned semiconductor wafer 100, through aprojecting optical system 124 and the aforementioned photochromic CELfilm 121. This exposure is accomplished by superposing the patterns withdifferent focal depths while using the FLEX method.

FIG. 95 presents the differences of the focal depths depending upon thepresence or absence of the photochromic CEL film 121 when the FLEXmethod is applied to the line-and-space pattern. FIG. 95(A) presents theoptical intensity profile of the exposure on the surface (or in thephotoresist film 120) of the semiconductor wafer 100 to theline-and-space pattern. As shown in FIG. 95(A), the portioncorresponding to the position, in which the chromium pattern 125A of thereticle 125 is absent, is irradiated with the light such that theoptical intensity is the maximum at the focal point (0 μm!) and becomesthe lower as vertically leaving the more from the focal point.

FIG. 95(B) present the relations between the optical intensity profileand the characteristic of the photochromic CEL film 121 in case the FLEXmethod is applied to move the surface of the semiconductor wafer 100vertically stepwise thereby to enhance the focal depth. If the surfaceof the semiconductor wafer 100 is moved upwards by 0.5 μm!, as shown inFIG. 95(B), (a) the optical intensity raises the position in which thephotoresist film 120 is deep. If this optical intensity reaches thepredetermined value at which the photochromic CEL film 121 is turnedtransparent, (b) the photoresist film 120 is irradiated with the lightin an amount exceeding the aforementioned constant amount. In case theaforementioned optical intensity is not more than the constant value,namely, in a shallow position of the photoresist film 120, the opticalirradiation is shielded by the photochromic CEL film 121. Next, if thesurface of the semiconductor wafer 100 is moved downwards by 0.5 μm!, asshown in FIG. 95(B), (c) the optical intensity has the higher value forthe shallower position of the photoresist film 120. When this opticalintensity reaches the constant value at which the photochromic CEL film121 is turned transparent, (d) the photoresist film 120 is irradiated inan amount exceeding the aforementioned constant amount. In case theaforementioned optical intensity is not higher than the constant amount,namely, in the deep position of the photoresist film 120, the opticalirradiation is shielded by the photochromic CEL film 121.

FIG. 95(C) presents the profile of the total optical intensity of thetwice optical irradiations in case the FLEX method shown in FIG. 95(B)is applied. In FIG. 95(C), the column (a+b) corresponds to the case inthe absence of the photochromic CEL film 121, and the column (a×b+c×d)corresponds to the case in the presence of the photochromic CEL film121. If, in the former case of the absence of the photochromic CEL film121, the FLEX method is applied to the line-and-space pattern, theoptical intensity profile exceeds the melting level of the photoresistfilm 120 in the unexposed portion so that the means is not suitable forimproving the focal depth. In the latter case of the presence of thephotochromic CEL film 121, the resolution and the focal depth can beimproved by the bleaching effect of the photochromic CEL film 121 and bythe change in the focal point by the FLEX method.

After the exposure step shown in FIGS. 91 and 92, the photochromic CELfilm 121 is removed <4> by a cleaning liquid 122, and the aforementionedphotoresist film 120 is developed <5> with a developing liquid 123.

As shown in FIG. 91, on the other hand, the photochromic CEL film 121Amay be used in place of the step of applying the photochromic CEL film121. This photochromic CEL material 121A is pushed, when used, againstthe surface of the photoresist film 120 which is applied to the surfaceof the semiconductor wafer 100.

Thus, in the photolithography, a high resolution and a large focal depthof the pattern can be achieved by using the FLEX method and the CELmethod.

(Embodiment XI)

In the fabrication process of the DRAM 1 of the foregoing embodiment I,the present embodiment XI is directed to an eleventh embodiment of thepresent invention, in which the alignment accuracies of the individuallayers are improved.

The structure of the semiconductor wafer 100 before the dicing step ofthe DRAM 1 according to the embodiment XI of the present invention isshown in FIG. 96 (presenting a schematic top plan view).

As shown in FIG. 96, the semiconductor wafer 100 is arrayed in a matrixshape with a plurality of DRAMs 1 before the dicing step (i.e., beforethe shaping into pellets). The not-shown scribe areas are formed betweenthe individual DRAMs 1. As shown in FIG. 97 (presenting an enlarged topplan view of the portion A of FIG. 96) and FIG. 98 (presenting anenlarged top plan view of a portion B of FIG. 97), the target marks TMto be shared between the adjoining DRAMs 1 are arranged in the scribeareas between the adjoining DRAMs (α to ε) of the semiconductor wafer100. Those target marks TM provide references for positioning thealignments in a reduced-scale projecting exposure device. As shown inFIGS. 97 and 98, the target marks TM to be shared between the adjoiningDRAMs 1, e.g., β and τ are so arranged that they can be detected by thesingle scanning of an alignment beam AB in the X direction. FIGS. 97 and98 show the waveforms of alignment signals S when the target marks TMare detected by the scanning with the alignment beam AB. On the basis ofthese alignment signals, the center position Xβ in the X direction, thecenter position Y β in the Y direction and the amount of rotation of theDRAM (β) shown in FIG. 97 can be calculated by the following equations:

    Xβ=(Xαβ+Xβτ)/2;

    Yβ=(Yβδ+Yε)/2; and

    Wβ=1/2 (Xβu-Xβl)/Cx=(Yβl -Yβr)/Cy!.

According to the alignment of the present embodiment XI, in case thepattern (i.e., pellet pattern) of the DRAM 1 of the second layer is tobe arranged with the pattern (i.e., pellet pattern) of DRAM 1 of thefirst layer arrayed on the surface of the semiconductor wafer 100, theposition of the target marks TM of the pattern of the first-layer DRAM 1is detected and calculated by the alignment beam AB so that the patternof the second-layer DRAM 1 is arranged while making a correction toreduce the positional displacement between the patterns of the adjoiningsecondlayer DRAMs 1. In other words, there is adopted the associativealignment method, in which the pattern of the second-layer DRAM 1 isassociatively aligned with respect to the pattern of the first-layerDRAM 1. This associative alignment method can retain the regularity ofthe patterns of the DRAM 1, as compared with the pellet alignmentmethod. In this pellet alignment method, the individual patterns of theDRAMs 1 on the surface of the semiconductor wafer 100 are repeatedlyaligned and exposed.

On the other hand, the aforementioned associative alignment system willnot cause serious alignment errors directly but can achieve a highalignment accuracy even in case the target marks TM are seriouslyerroneously detected.

Moreover, the associative alignment method can achieve a higheralignment accuracy than the multipoint wafer alignment method even incase the array of the pattern of the first-layers DRAM 1 is highlydistorted. In the multi-point wafer alignment method, the plural targetmarks TM on the surface of the semiconductor wafer 100 are sampled andaligned so that the array of the DRAMs 1 is estimated from thestatistical calculations of the alignment result until only the exposureis accomplished.

In the aforementioned alignment method, moreover, on the basis of thedetections of the target marks TM arranged at the four sides of thepattern of the first-layer DRAMs 1, the amount of rotation of thepattern of the second-layer DRAMs 1 can be calculated and corrected. Asa result, a higher correction accuracy of the amount of rotation can beachieved than that of the case in which the target marks TM arranged attwo higher and lower points or two righthand and lefthand points of theDRAMs 1 are to be detected to correct the amount of rotation. Even inthe case of the correction of the amount of rotation, the associativealignment method causes no direct large correction errors of the amountof rotation, even if one target mark TM is erroneously detected, so thata high alignment accuracy can be achieved.

In case, on the other hand, the aforementioned pellet alignment methodand multi-point wafer alignment method are mixed, the alignment accuracyis generally dropped. However, the associative alignment method canachieve a high alignment accuracy even in case it is mixed with eithermethod.

Moreover, the aforementioned associative alignment method can detect thetarget marks TM of the pattern of the adjoining two DRAMs 1 can bedetected by the single scanning of the alignment beam AB so that athroughput substantially similar to that of the aforementioned pelletalignment method can be attained.

FIG. 99 shows the comparisons of the individual alignment accuraciesamong the associative alignment method, the pellet alignment method andthe multipoint wafer alignment method in case the array of the patternof the first-layer DRAMs 1 are distorted or rotated. In FIG. 99(A), (a)shows the ideal array of the pattern (1) of the first-layer DRAMs 1, and(b) shows the individual arrays in case there are array strains androtations in the pattern (1) of the fistlayer DRAMs 1. In the pattern(1) of the latter first-layer DRAMs 1: the individual X coordinates ofthe DRAMs α to τ are not coincident; the individual pitches of the DRAMsα and β and the DRAMs β and τ in the Y direction are different; and theDRAMs α and τ individually have rotational errors. These array strainsand rotations are caused by the warp which is established in thesemiconductor wafer 100 by the repeated heat treatments.

FIG. 99(B) shows the comparisons of the individual alignments when thepattern (2) of the second-layer DRAMs 1 are aligned in case theaforementioned array strains and rotations are in the array of thepattern (1) of the first-layer DRAMs 1. In either case, the pattern (2)of the second-layer DRAM τ shows the case in which the target marks TMare seriously erroneously detected with respect to the pattern (1) ofthe first-layer DRAM τ. On the other hand, the amount of rotation iscalculated in the associative alignment method on the basis of thedetections of the four target marks TM and in the other two alignmentmethods on the basis of the detections of the two target marks TM. Incase the correction is and is not made on the amount of rotation, asshown in FIG. 99(B), the associative alignment method can achieve ahigher alignment accuracy than the other pellet alignment method andmulti-pint wafer alignment method.

Thus, the high alignment accuracy can be attained by adopting theassociative alignment method.

(Embodiment XII)

In the DRAM 1 of the foregoing embodiment I, the present embodiment XIIis directed to a twelfth embodiment of the present invention, in whichthe reliability is improved at the connected portions between thetransition-metal film to be buried in the connecting holes of theinterlayer insulating film by the selective CVD method and the wiringlines extending over said interlayer insulating film.

The structure of the DRAM 1 according to the embodiment XII of thepresent invention is shown in FIG. 100 (presenting an essential portionin section).

In the DRAM 1 of the present embodiment XII, as shown in FIG. 100, thetransition-metal film 54 is buried in connecting holes 51D and SISformed in the interlayer insulating film 51 and is connected with thewiring lines 52 extending over the interlayer insulating film 51.

In the region of the memory cell array 11E, there are arranged thememory cells M which are composed of the memory cell selecting MISFETsQs and the information storing capacity elements C of the stackedstructure, so that the region has a larger stepped shape than that ofthe regions of the peripheral circuits. As a result, the interlayerinsulating film 51 has a thinner memory cell array 11E than the regionsof the peripheral circuits. As shown in FIG. 100 and FIG. 101(presenting an essential portion at a predetermined fabrication step insection), the connecting holes 51S formed in the memory cell array 11Eof the interlayer insulating film 51 are made shallow, whereas theconnecting holes 51S formed in the regions of the peripheral circuitsare made deep.

The aforementioned transition-metal film 54 used is formed of the W filmwhich is deposited by the selective CVD method like the foregoingembodiment I. The wiring lines 52 used are formed of an aluminum alloyfilm in the present embodiment XII. On the other hand, the wiring lines52 may be exemplified by either a transition-metal film such as the Wfilm deposited by the sputtering method or a composite film composedmainly of the former.

The transition-metal film 54 is formed to have such a thickness as tobury the shallow connecting holes 51S of the regions of the memory cellarray 11E, as shown in FIGS. 100 and 101. In other words, thetransition-metal film 54 is so formed with reference to the shallowconnecting holes 51S that it may not protrude from the connecting holes51S. In case the transition-metal film 54 highly protrude from theconnecting holes 51S, the surfaces of the wiring lines 52 thereoverprotrude so that the size of the etching mask is changed from the setvalue to drop the treating accuracy of the wiring lines 52 as a resultof the thickness dispersions and the diffractions of the photoresistfilm for treating the wiring lines 52. Since, moreover, thetransition-metal film 54 highly protruding from the aforementionedconnecting holes 51S cannot be covered with the overlying wiring lines52, they are etched more than necessary at the etching step of thewiring lines 52. The transition-metal film 54 to be buried in the deepconnecting holes 51D of the regions of the peripheral circuits is buriedto have such a thickness that the aspect ratio at the connecting holes51D may not exceed 1, as shown in FIG. 100. In case the aspect ratioexceeds 1, the step coverage of the overlying wiring lines 52 is droppedto cause the disconnections of the wiring lines 52 frequently at theconnecting holes 51D.

Thus, in the DRAM 1 in which the interlayer insulating film 51 is formedover the underlying surface having the stepped shape so that the shallowconnecting holes 51S are formed in the regions (of the memory cell array11E) having the high stepped shape of said underlying surface of theinterlayer insulating film 51 whereas the deep connecting holes 51D areformed in the regions (of the peripheral circuits) having the lowstepped shape and in which the wiring lines 52 are so extended over theinterlayer insulating film 51 that they are connected with thetransition-metal film 54 buried in the aforementioned connecting holes51S and 51D, the transition-metal film 54 to be buried in theaforementioned shallow connecting holes 51S and the aforementioned deepconnecting holes 51D is deposited by the selective CVD method, and thetransitionmetal film 54 is deposited to have a thickness substantiallyequal to the depth of the aforementioned shallow connecting holes 51S.Thanks to this construction, the transition-metal film 54 to be buriedin the aforementioned shallow connecting holes 51S and theaforementioned deep connecting holes 51D is formed to have a thicknesssubstantially equal to the depth of the shallow connecting holes 51S sothat it is precluded from protruding from the shallow connecting holes51S and the deep connecting holes 51D. As a result, it is possible toimprove the treating accuracy and reliability of the aforementionedwiring lines 52.

(Embodiment XIII)

In the DRAM 1 of the foregoing embodiment I, the present embodiment XIIIis directed to a thirteenth embodiment of the present invention, inwhich the reliability of the wiring lines 52 formed mainly of atransition-metal film.

The structure of the DRAM 1 according to the embodiment XIII of thepresent invention is shown in FIG. 102 (presenting an essential portionin section).

As shown in FIG. 102, the DRAM 1 of the present embodiment XIII has itswiring lines 52 extending over the interlayer insulating film 51. Thewiring lines 52 are formed of the composite film which is prepared bylaminating over the transition-metal film 52A the transition-metal film52B made of a substantially identical metal material.

The lower transition-metal film 52A of the wiring lines 52 is formed ofa W film deposited by the sputtering method, for example, to have athickness of about 80 to 129 nm!, for example. This lowertransition-metal film 52A has a high adhesiveness to the underlyinginterlayer insulating film (e.g., the silicon oxide insulating film) 51.Moreover, the lower transition-metal film 52A is formed to have theabove-specified thickness, because a too much thickness will cause anoverhang over the stepped shape formed by the connecting holes 51C andaccordingly the formation of cavity and the drop of the step coverage ofthe upper transition-metal film 52A. Still moreover, the lowertransition-metal film 52A is deposited by using a target voltageestablishing no film stress (i.e., within an allowable range at or neatthe stress 0), because it will cause the separation from the surface ofthe interlayer insulating film 51, as seen from the relation between thetarget voltage and the film stress when in the sputtering operation inFIG. 103. Furthermore, the lower transition-metal film 52A has anetching rate substantially equal to that of the upper transition-metalfilm 52B. Furthermore, the lower transition-metal film 52A can have itscontact resistance reduced because it has a higher corrosion resistancethan that of the TiN film and a small work function difference from theSi.

The upper transition-metal film 52B of the aforementioned wiring lines52 are made of the W film, which is deposited by the CVD method, to havea thickness of about 250 to 350 nm!, for example. This uppertransition-metal film 52B reduces the substantial resistance of thewiring lines 52 and constitutes a major component of the wiring lines52. The upper transition-metal film 52B can improve the reliability asthe wiring lines because the it is deposited by the CVD method to have ahigh step coverage at the underlying stepped portions thereby to reducethe defects such as the disconnections. The upper transition-metal film52B can have a high contactness with the underlying lowertransition-metal film 52A because it is made of an identical metal filmmaterial.

Thus, in the DRAM 1 in which the wiring lines 52 are formed of thetransition-metal film 52B deposited over the underlying interlayerinsulating film 51, the transition-metal film 52A of substantially thesame kind as the aforementioned transition-metal film 52B deposited bythe sputtering method is sandwiched between the aforementionedinterlayer insulating film 51 and the transition-metal film 52B of theaforementioned wiring lines 52. Thanks to this construction, the lowertransition-metal film 52A deposited by the sputtering method has highcontactnesses with the underlying interlayer insulating film 51 and theupper transition-metal film 52B of the wiring lines 52 so that it canimprove the contactness between the underlying interlayer insulatingfilm 51 and the wiring lines 52. Since the lower transition-metal film52A deposited by the sputtering method is formed of the transition-metalfilm of substantially the same kind as that of the overlyingtransition-metal film 52B, the treated side walls of the wiring lines 52can be prevented from being roughed to improve the treating accuracy ofthe wiring lines 52.

In case the lower transition-metal film 52A of the wiring lines 52 isconnected directly with the n⁺ -type semiconductor region 32 and the p⁺-type semiconductor regions 39, as shown in FIG. 102, the heat treatmentafter the deposition of the lower transition-metal film 52A isaccomplished at such a temperature or lower that the W and the Si willnot alloy. Specifically, the heat treatment is accomplished at about 600° C.! or lower. Thus, by restricting the heat treating temperature ofthe lower transitionmetal film 52A of the aforementioned wiring lines52, the resistance of the connected portions due to the alloyingreaction between the aforementioned W and Si is suppressed from rising,to prevent the alloy spike phenomena.

(Embodiment XIV)

In the DRAM 1 of the foregoing embodiment I, the present invention XIVis directed to a fourteenth embodiment of the present invention, inwhich the reliabilities at the connected portions between the individualelements and the wiring lines are improved.

The structure of the DRAM 1 according to the embodiment XIV of thepresent invention is shown in FIG. 104 (presenting an essential portionin section).

In the DRAMs 1 of the present embodiment XIV, as shown in FIG. 104, inthe memory cell array 11E, an intermediate conducting film 130 isinterposed between one of the n-type semiconductor regions 29 of thememory cell selecting MISFETs Qs of the memory cells M and thecomplementary data lines (DL) 50. This intermediate conducting film 130is partially connected with the n-type semiconductor regions 29 throughthe connecting holes 131A formed in an interlayer insulating film 131and the connecting holes 34A and is partially extended over the sidewall spacers 31 and the interlayer insulating film 131. In theconnecting holes 131A formed in the interlayer insulating film 131, theconnecting holes 34A are formed by the side wall spacers 31, which areformed in the side walls of the gate electrodes 27 of the memory cellselecting MISFETs Qs, to define the opening size. Since the connectingholes 34A are formed in self-alignment with the gate electrodes 27, theconnections between the intermediate conducting film 130 and the n-typesemiconductor regions 29 are accomplished in self-alignment with thegate electrodes gate electrodes 27. In short, the n-type semiconductorregions 29 of the memory cell selecting MISFETs Qs and the complementarydata lines 50 are connected through the intermediate conducting film 130and in self-alignment-with the gate electrodes 27 of the memory cellselecting MISFETs Qs.

The intermediate conducting film 130 is formed above the gate electrodes27 (including the word lines 27) of the memory cell selecting MISFETs Qsand below the lower electrode layer 35 of the information storingcapacity element C of the stacked structure. Specifically, the lowerelectrode layer 35 of the information storing capacity element C of thestacked structure is formed to have the large thickness so as toincrease the amount of charge storage so that the intermediateconducting film 130 is formed separately of and below the lowerelectrode layer 35 so as to improve the treating accuracy. Theintermediate conducting film 130 is formed of the polycrystallinesilicon film, which is deposited by the CVD method, for example, to havea small thickness of about 80 to 120 nm!, for example. Thispolycrystalline silicon film is doped with an n-type impurity to reducethe resistance.

The intermediate conducting film 130 can damp especially the steepstepped shape of the connected portions of the memory cells M and thecomplementary data lines 50 so that it can reduce the defects, i.e., thedisconnections of the complementary data lines 50.

The intermediate conducting film 130 is formed in the elements of theperipheral circuits, too, at the common fabrication step. Although notlimitative thereto, in the present embodiment XIV, the intermediateconducting film 130 is formed in the regions of the n-channel MISFETs Qnrequiring an especially strict layout rules between the n⁺ -typesemiconductor regions 32 and the wiring lines 52. Usually, theperipheral circuits have looser layout rules than the memory cell arrays11E. Even in case the wiring lines 52 ride on the element separatinginsulating film 23 in the regions of the peripheral circuits, as shownin FIG. 104, the intermediate conducting film 130 can be formedinbetween to connect the n⁺ -type semiconductor regions 32 and thewiring lines 52 reliably to improve the degree of integration of theDRAMs 1 resultantly. Even in case the n-channel MISFETs Qn and thep-channel MISFETs of the peripheral circuits are connected through thewiring lines 52 which are made of a material for facilitating the mutualdiffusions of the impurities such as the transition-metal film, too, theintermediate conducting film 130 can prevent the aforementioned mutualdiffusions to reduce the resistance at the connected portions.

Next, the process of forming the DRAM 1 according to the presentembodiment XIV will be briefly described with reference to FIGS. 105 and106 (presenting essential portions at the individual fabrication stepsin section).

First of all, the memory cell selecting MISFETs Qs of the memory cells Mand the n-channel MISFETs Qn of the peripheral circuits are individuallyformed like the process for forming the DRAM 1 of the foregoingembodiment I.

Next, the interlayer insulating film interlayer insulating firm 131 isso deposited all over the surface of the substrate as to cover theaforementioned memory cell selecting MISFETs Qs and n-channel MISFETsQn. The interlayer insulating film 131 used is formed of the siliconoxide film, which is deposited by the CVD method using inorganic silanegases and nitrogen oxide gases, for example, as its source gases, tohave a thickness of about 40 to 60 nm!.

Next, the connecting holes 131A and the connecting holes 34A are formedin the aforementioned inter-layer insulating film 131 in the individualregions, i.e., one of the n-type semiconductor regions 29 of the memorycell selecting MISFETs Qs of the memory cells M and the n⁺ -typesemiconductor regions 32 of a predetermined one of the n-channel MISFETsQn.

Next, as shown in FIG. 105, there is formed the intermediate conductingfilm 130 which is to be connected through the aforementioned connectingholes 131A and 34A with the n-type semiconductor regions 29 and the n⁺-type semiconductor regions 32.

Next, as shown in FIG. 106, the interlayer insulating film 33 is formedall over the surface of the substrate including the surface of theintermediate conducting film 130. After this, the DRAMs 1 of the presentembodiment XIV is completed by accomplishing the steps similar to thoseof the process of forming the DRAMs 1 of the foregoing embodiment I suchas the information storing capacity element C of the stacked structureor the p-channel MISFETs Qp. Thus, in the DRAMs 1 in which there arearranged the memory cells M which are formed of a series circuit betweenthe memory cell selecting MISFETs Qs and the information storingcapacity element C of the stacked structure having the lower electrodelayer 35, the dielectric film 36 and the upper electrode layer 37 at theintersections between the complementary data lines 50 and the gateelectrodes 27, there is formed between the complementary data lines 50and one of the n-type semiconductor regions 29 of the memory cellselecting MISFETs Qs the intermediate conducting film 130 which ispartially formed in self-alignment with said one of the n-typesemiconductor regions 29, which is partially extracted to above the gateelectrodes 27 of the memory cell selecting MISFETs Qs and which isformed below and separately of the lower electrode layer 35 of theinformation storing capacity element C of the stacked structure. Thanksto this construction, the intermediate conducting film 130 is sandwichedso that the area of the memory cells M can be reduced to improve thedegree of integration to an extent corresponding to the maskingallowance at the fabrication step between the one of the n-typesemiconductor regions 29 of the memory cell selecting MISFETs Qs and thecomplementary data lines 50. At the same time, the gap between theintermediate conducting film 130 and the lower electrode layer 35 of theinformation storing capacity element C of the stacked structure can beeliminated to increase the area of the lower electrode layer 35independently of the intermediate conducting film 130. As a result, theamount of charge storage of the information storing capacity element Cof the stacked structure can be increased to reduce the area of thememory cells M thereby to improve the degree of integration.

Moreover, the intermediate conducting film 130 is constructed to have asmaller thickness than that of the lower electrode layer 35 of theinformation storing capacity element C of the stacked structure. Thanksto this construction, the information storing capacity element C of thestacked structure can increase the thickness of the lower electrodelayer 35 to enlarge the area in the vertical direction so that theamount of charge storage can be improved to shrink the area of thememory cells M thereby to improve the degree of integration. At the sametime, the intermediate conducting film 130 is made thin so that it canbe simply treated.

Between the n⁺ -type semiconductor regions 32 of the n-channel MISFETsQn constituting the peripheral circuits and the wiring lines 52 to beconnected with the former, moreover, there is interposed theintermediate conducting film 130 which is formed of the same conductinglayer as that of the intermediate conducting film 130 formed in theaforementioned memory cells M. Thanks to this construction, theintermediate conducting film 130 of the peripheral circuits can beformed at the step of forming the intermediate conducting film 130 inthe memory cells M of the DRAM 1 so that the number of fabrication stepsof the DRAM 1 can be reduced.

Although our invention has been specifically described hereinbefore inconnection with the foregoing embodiments thereof, it should not belimited to the foregoing embodiments but can be modified in variousmanners without departing the gist thereof.

For example, the present invention can be applied to a semiconductorintegrated circuit device such as a microcomputer using the DRAM as itsone unit.

The present invention should not be limited to the aforementioned DRAMbut can also be applied to a semiconductor integrated circuit devicesuch as the SHAM or the ROM having storing functions.

Moreover, the present invention can be applied to a multi-layered wiringtechnology for the printed wiring substrate or the like.

The effects to be attained by the representatives of the invention thusfar disclosed will be briefly described in the following:

(1) The degree of integration of the semiconductor integrated circuitdevice having the storing functions can be improved;

(2) The electric reliability of the aforementioned semiconductorintegrated circuit device can be improved;

(3) The soft error withstand voltage of the aforementioned semiconductorintegrated circuit device can be improved;

(4) The number of fabrication steps of the aforementioned semiconductorintegrated circuit device can be reduced;

(5) The treating accuracy for fabricating the aforementionedsemiconductor integrated circuit device can be improved;

(6) The drivability of the semiconductor elements of the aforementionedsemiconductor integrated circuit device can be improved;

(7) The fabrication yield of the aforementioned semiconductor integratedcircuit device can be improved;

(8) The operating speed of the aforementioned semiconductor integratedcircuit device can be increased;

(9) The wiring defects, e.g., the disconnections of the aforementionedsemiconductor integrated circuit device can be prevented;

(10) The moisture resistance of the aforementioned semiconductorintegrated circuit device can be improved;

(11) In the aforementioned semiconductor integrated circuit devicehaving the redundancy fuses, the step of forming the redundancy fusescan be simplified;

(12) The quality of the films to be used in the aforementionedsemiconductor integrated circuit device can be improved; and

(13) The apparatus for fabricating the item (12) can be provided.

What is claimed is:
 1. A method of forming a semiconductor integratedcircuit device having a memory array, direct peripheral circuitry and anoutput buffer circuit, said direct peripheral circuitry including afirst MISFET to which a first operating voltage is applied, and saidoutput buffer circuit including a second MISFET to which a secondoperating voltage, higher than the first operating voltage, is applied,said method comprising the steps of:providing a semiconductor substratehaving a main surface, the semiconductor substrate including a firstportion for said first MISFET and a second portion for said secondMISFET; forming a first gate insulating film in said first portion and asecond gate insulating film in said second portion; forming a first gateelectrode on said first gate insulating film in said first portion and asecond gate electrode on said second gate insulating film in said secondportion, said first and second gate electrodes having side surfaces;introducing first impurities of a first conductivity type into saidfirst and second portions in a self-aligned manner with said first andsecond gate electrodes, respectively; forming sidewall spacers on saidside surfaces of said first and second gate electrodes, said sidewallspacers on said side surfaces of the first gate electrode having a samewidth as a width of the sidewall spacers on the side surfaces of thesecond gate electrode; and introducing second impurities of the firstconductivity type into said first and second portions in a self-alignedmanner with said sidewall spacers, wherein a length of the second gateelectrode is longer than that of said first gate electrode.
 2. A methodof forming a semiconductor integrated circuit device according to claim1, wherein said first operating voltage is 3.3 V and said secondoperating voltage is 5 V.
 3. A method of forming a semiconductorintegrated circuit device according to claim 1, including the furthersteps of connecting the first MISFET to a source of the first operatingvoltage and connecting the second MISFET to a source of the secondoperating voltage which is higher than the first operating voltage.
 4. Amethod of forming a semiconductor integrated circuit device according toclaim 3, wherein the first operating voltage is 3.3 V and the secondoperating voltage is 5 V.
 5. A method of forming a semiconductorintegrated circuit device according to claim 1, wherein saidsemiconductor integrated circuit device includes a dynamic random accessmemory.
 6. A method of forming a semiconductor integrated circuit deviceaccording to claim 1, wherein said length of the second gate electrodeis about 8 μm, and said length of the first gate electrode is in a rangeof 0.8-1.4 μm.
 7. A method of forming a semiconductor integrated circuitdevice according to claim 1, wherein said direct peripheral circuitry isa sense amplifier circuit.
 8. A method of forming a semiconductorintegrated circuit device having a memory array, direct peripheralcircuitry and an output buffer circuit, said direct peripheral circuitrycomprising a first MISFET having a first gate electrode and first sourceand drain regions, and to which a first operating voltage is applied,and said output buffer circuit comprising a second MISFET, having asecond gate electrode and second source and drain regions, and to whicha second operating voltage, which is higher than the first operatingvoltage, is applied, the method comprising the steps of:providing asemiconductor substrate having a main surface, the semiconductorsubstrate including a first portion for said first MISFET and a secondportion for said second MISFET; forming a gate insulating film on saidmain surface of the semiconductor substrate in said first and secondportions; depositing a conductive film over said gate insulating film;forming said first gate electrode in said first portion and said secondgate electrode in said second portion, by patterning said conductivefilm, said first and second gate electrodes having side surfaces;implanting first impurities of a first conductivity type into said firstand second portions at first parts not covered with said first andsecond gate electrode, in order to form first semiconductor regions atboth sides of said first and second gate electrodes; depositing aninsulating film over said first and second gate electrodes; performinganisotropic etching of said insulating film in order to form sidewallspacers on said side surfaces of said first and second gate electrodes;and implanting second impurities of the first conductivity type intosaid first and second portions at second parts not covered with saidfirst and second gate electrodes and not covered with said sidewallspacers, in order to form second semiconductor regions at both sides ofsaid first and second gate electrodes, wherein said first source anddrain regions and said second source and drain regions each comprisesaid first and second semiconductor regions, and a length of the secondgate electrode in a direction of current flow is longer than a length ofsaid first gate electrode in a direction of current flow.